IMO, the best bargain for a new buggy would be a Mugen MBX5 at $300 + shipping from amainhobbies.com (using this coupon code CALPJAN825 for $25 off of $250 or more). You won't find a cheaper 1/8th buggy that already has conversion parts available for it. Aside from that, parts are widely available and usually can be found cheap on eBay from chop shops.
How about an Ofna Hyper 7 TQ Sport? Only $180 on the homepage of http://nitrohouse.com/ . Since you havne't listed whether it's for racing or bashing, the Hyper 7 will work well for bashing.
SH Z-Car, Custom Crawler, 8s Savage, 12s XTM XLB 1/7 buggy, 4wd 4-link rear/IFS Pro4 truck, Custom Hyper 10 Short Course, Belt-Drive Mammoth ST 1/8 truggy, 4s 17.5 MM Pro HPI Blitz