WHMCS is only $9 - $13 per month depending if you buy it from a reseller, i recommend getting it from
http://www.whmcslicenses.com as its only $10 from them, i could modify Ihost for you to allow use on reseller accounts, as i have done it in th past to test see if it worked, but to modify it for you and give you the modded version i would need permission from the original coders and proof of your purchase... When i done it to test it there was only 1 bug that i found, and that was the fact that it displays all the packages on the server (you cant actually use the packages unless you created them though)
Also i have my own account creation software for cpanel, its very basic and there isnt a billing or support system with it, its strictly for free accounts, but can be easily integrated with a billing system or support system, and can be very easily integrated with your design
Let me know if you want me to send it you (FREE)
Cheers