If you have a problem with power try switching to Nvidia some card have lower power consuption than others. Otherwise i'll stick to ATI radeon ones. Do not take requirements so hard, they always put higher value of power consuption than it realy needs. People have no problem with runing HD 7750 with 300W psu. But u need to be carefull, some psu-s are ***** bad and it's not worth pushing them to the limit. You can damage your PC. You should check your model of psu and tell us. But still it will be wise to buy new psu to avoid risk. You can find good cpu-s (let's say 600W) for good price! I'm sure you'll find something that fit with ur budget.
With upgraded psu you can also think about more powerfull cards HD 5850. The choise is yours. Sorry for my bad English. Hope you'll understand.