First of all, a disclaimer: ask a pile of interested people very carefully before deciding on prices; people suck at accurately saying how much they'd pay for something, and that almost certainly includes me. :) If you want to get fancy about it, take a look at https://en.wikipedia.org/wiki/Van_Westendorp%27s_Price_Sensi... , and perhaps http://www.priceintelligently.com/ ; if you don't want to get fancy about it, just make sure you talk to more than a few people.
That said: I actually think $4 would work nicely as a "project" price, and for more along the lines of 1 week rather than 2 months. That would nicely cover immediate one-time pain like the case I ran into. $4 falls squarely in the category of "yeah, I'll pay that to solve this problem today", and I'd have paid that just for the 1 day I needed to use it.
If you feel like you can comfortably serve people at $4/month, I'd absolutely pay that price without hesitation; $7/month seems reasonable too. Perhaps you should just treat that as the "project" case, and market it so that people think of it more as a "pay once and use it for a month" price than something they necessarily have to pay repeatedly for via a subscription. I think that'd make more sense than trying to go off the beaten path by talking about weeks. :) (Most "monthly" services don't really cater for the case of "let it lapse, then start paying again when I need it", but in the case of this project I think it would work beautifully to do so several times a year.)
I don't have a strong feeling for the right price for a year. You want something that makes people say "I'll use it often enough that I don't just want to pay $4 (or $7) each time I use it." You might just want to start with monthly and add annual if someone asks for it. Annual billing also introduces new complications, such as making chargebacks more frequent and more serious.
I also think some great opportunities exist here for "organization" or "college department" plans. I could easily imagine an entire CS department getting enough value out of this to pay for it, if you don't mind jumping through the hoops it takes to sell to such entities.
Regarding queuing: Redis works beautifully for this. Just add the ID for the particular version of the project to a queue when the user hits the PDF button (Redis: LPUSH), and run a pile of queue processors, each of which grabs an ID from the queue (Redis: BRPOP) and runs pdflatex. To handle premium users, use a separate queue with some queue processors only looking at that queue and some looking at both. (BRPOP accepts multiple lists and returns an item from the first non-empty list.) Track the processing time for premium and free users, and throw enough resources at queue processors to get each of those to the level of service you want to provide.
Regarding payment: words can't express how much I'd recommend against PayPal. But then, I have access to things like Stripe and Samurai; sorry. :( I'd still recommend finding a decent payment gateway if possible. You'll also find it a lot harder to sell to organizations or departments if you use PayPal.
Interesting on redis, I already use it to store sessions. A friend talked about have 2 ques, only process free que when premium is empty as well.
When I get a chance to breath I will look into the price levels in more detail.
I would ideally look for a provider who can just take all the hassle out of taking cards and doing reoccurring payments. Sorting out a payment gateway is a lot of effort which I would rather focus on the product in the short term (next 3 months).
That said: I actually think $4 would work nicely as a "project" price, and for more along the lines of 1 week rather than 2 months. That would nicely cover immediate one-time pain like the case I ran into. $4 falls squarely in the category of "yeah, I'll pay that to solve this problem today", and I'd have paid that just for the 1 day I needed to use it.
If you feel like you can comfortably serve people at $4/month, I'd absolutely pay that price without hesitation; $7/month seems reasonable too. Perhaps you should just treat that as the "project" case, and market it so that people think of it more as a "pay once and use it for a month" price than something they necessarily have to pay repeatedly for via a subscription. I think that'd make more sense than trying to go off the beaten path by talking about weeks. :) (Most "monthly" services don't really cater for the case of "let it lapse, then start paying again when I need it", but in the case of this project I think it would work beautifully to do so several times a year.)
I don't have a strong feeling for the right price for a year. You want something that makes people say "I'll use it often enough that I don't just want to pay $4 (or $7) each time I use it." You might just want to start with monthly and add annual if someone asks for it. Annual billing also introduces new complications, such as making chargebacks more frequent and more serious.
I also think some great opportunities exist here for "organization" or "college department" plans. I could easily imagine an entire CS department getting enough value out of this to pay for it, if you don't mind jumping through the hoops it takes to sell to such entities.
Regarding queuing: Redis works beautifully for this. Just add the ID for the particular version of the project to a queue when the user hits the PDF button (Redis: LPUSH), and run a pile of queue processors, each of which grabs an ID from the queue (Redis: BRPOP) and runs pdflatex. To handle premium users, use a separate queue with some queue processors only looking at that queue and some looking at both. (BRPOP accepts multiple lists and returns an item from the first non-empty list.) Track the processing time for premium and free users, and throw enough resources at queue processors to get each of those to the level of service you want to provide.
Regarding payment: words can't express how much I'd recommend against PayPal. But then, I have access to things like Stripe and Samurai; sorry. :( I'd still recommend finding a decent payment gateway if possible. You'll also find it a lot harder to sell to organizations or departments if you use PayPal.