CFL's produce 0.3grams per watt of squared feet when used with proper spacing. I believe the spacing is uhh something like 5,000 lumens per square meter. OK wait...I just confused the shit outta myself. Lemme rephrase.

CFL is 0.3grams per watt compared to 1gram per watt of HPS (for flowering). The difference from CFL and MH for the vegative state is how fast and healthy the plant grows (hence allowing for even more yield.)

Hope this helps.

Basically, in your situation, CFLs are the only option you have (if those even work for it).