Funny you say that after you've edited one post of yours where you remove information stating that whmcs is beyond your budget. I simply pointed out there was an existing solution, that is used by many, and does a pretty decent job for a very minimal expenditure. Further pointed out that for that petty investment, you're not likely to find something equivalent or better for that amount.
Now, you go on to say I'm being ignorant which is quite contrary if you think about how well written the code would be to accomplish what you'd like on such a finite budget. I'm sure that $15 worth of php code could get you all the things you want with profound measures in place to protect better than a team with a community (sarcasm intended).
Back on topic, good luck to you and I'll enjoy looking for your implemented product after its completion.