Don't let the hate get to you. I'm not sure what the wattage is on a 5750, but on a 5770 it's about 2:1 mh/j. They're small but stout.
I'm not good with numbers, but if it's doing 150 to 175 Mhash/s at ~100 watts, that's 1.5 to 1.75 Mh/J, right?
The 5750 was $100 at a local store, and there was a $25 mail-in manufacturer's rebate (HIS brand). A new 5750 was purchased and taken right back: the store kindly applied the rebate price to it plus knocked more off for being "used", so I got to purchase it for extra cheap.
I used it to upgrade an old system that had an 8600 GT (6 Mhash/s).