What makes you think that road bars won't do? The bars you currently have are probably 25.4mm, just like many road drop bars. Brifters aren't always expensive either. The prices are coming down. Here are 7-speed/triple shifters for $78 on ebay:
Shimano RSX St A410 STI Shifters Road Bike 7 SP 7 Speed Triple | eBay
You would just need those, drop bars, a 7-speed freewheel/cassette, bar tape, and new cables.