Here's a 7-speed right-hand lever for $36:

http://www.ebay.com/itm/Shimano-Sora...202#vi-content

And a 3-speed left-hand lever for $39:

http://www.ebay.com/itm/Shimano-SORA...2202%26ps%3D54

I know, Sora is kinda frowned upon since it upshifts with buttons, but add a Shimano Road front triple derailleur and you'll be under a C-note. And it will be perfectly functional.