It's not so super commercial project but if whole profit from game was about 100$/month, that would be nice. And maybe we wouldn't even like to play with all those formal agreements etc. Is that possible to let them just have a track of game profits so that they would be sure I'm not cheating? Maybe grant them access to profit statistics from the advertisement provider for example? We will more likely search for something like this I guess
A couple points..
This is your idea and you are driving it. That means you get the lion's share of 'profits' (regardless of how large or how small). That is also reflected in how many hours you've spent creating the engine, etc.
The easiest/cleanest thing to do is to pay people flat fee, period. They give you stuff--you pay them money and you're done with it.
The reason for sharing 'profits' is either
a) you are a generous soul
b) you want to reduce your out of pocket expense.
By having someone create work for a 'share of the profits' (sometimes known as 'back end'), you are asking them to take on more risk-- There's virtually no risk in doing a job for a flat fee; there's lots of risk in sharing in the profits. So if you are asking them to take on more risk, there should be more reward for them.
ballpark I'd say keeping 80% of the profits for yourself, should decide to go down that route, isn't unreasonable.
And maybe we wouldn't even like to play with all those formal agreements etc
You're playing with fire there. I get that a lawyer is expensive. And no fun. And it seems like a waste..
The problem is that this stuff gets complicated fast-- what exactly are "profits"? is that before or after things like web fees, marketing. Exactly who owns what? How is it that we can check to see if you're cheating us or not?
Odds are that won't be a problem, but say your game takes off? Or is bought by someone? Or you do it for another platform?
At the very least, have one clear, concise email summarizing exactly who gets paid what. Write this as a separate email AFTER you've come to agreement. Do not make it part of an email chain (the danger there is that you are thinking something 5 emails down still applies, but the artist doesn't, etc.).
Is that possible to let them just have a track of game profits so that they would be sure I'm not cheating? Maybe grant them access to profit statistics from the advertisement provider for example?
This is usually taken care of in a clause in the contract
that gives the others the right to audit you.
Bottom line-- like it not, when you create a game and put it out for the world to see (and buy), you have created a business. And if you have used other people to help create that game, then you have entered into business relationships with those people. And when you do that, a contract is everybody's best friend.