The reason case/PSU combos are cheaper is because the PSUs are usually junk. I'd advise against that choice. If you are going to go with a 500W PSU, pick one from the top 2 tiers in this list: https://community.newegg.com/eggxpert/computer_hardware/f/135081/t/45344.aspx?Redirected=true
If you insist on going the combo route, go with the Zalman combo. It has slightly better +12V ratings.