Are you looking to stand out from the others with a custom portal .. or one that appears custom?
Let's face it, WHMCS has the goods so why try to reinvent the wheel. Instead of laying down all your benjies on a custom coded portal, just get WHMCS pimped out with a custom skin.
Okay that was fun and all ... we generally don't talk like that (well, not all the time) ... but getting serious now, if you are looking to have a billing system with a custom feel to it then holla! (wow it's addicting).
We have done some amazing work for companies such as VOIPo, HostNine, Eleven2, and many many others.
Hit us with a PM and we will get back with you on a quote. Generally prices range anywhere from as low as $500 and up depending on the level of custom work.
Just so you know, we have been known to delete WHMCS's template style sheets and rework their code completely and welcome in table-less templates.