If it's an 18 series PIC then a C compiler is available (30 day trial, or 'student edition', but continues to work after 30 days with some optimisations turned off) from microchip.com website.
Installs into MPLAB and all works a treat. But a hardware emulator (RfSolutions ICEPIC3 here) doesn't half make things easier!
DUDE.... mikroc from mikroelektronika... it's the best C compiler for PICs out there. The shareware version has a 2K limit but even then it's still more than enough. If you're using 18f452 or an 18F family chip, then mikroC is really the BEST (IMHO) compiler out there.
Have you checked out http://www.sourceboost.com/
The free license version has very few restrictions which are
12F/16F 2 RAM banks 2k code
18F 2 RAM banks 4k code
It supports all of the chips the full version (which only costs about $150us) and it has good support.
And so far I have not encountered any major problems with it's C support...