How much does it cost to get tested for STDS?

It doesn't coast anything at a clinic if your insurance covers it
There are some organizations and clinics that offer affordable STD testing. (Planned Parenthood)

Other places offer FREE testing, but it really depends on your area. I know Los Angeles County has various free testing sites. I recommend you do a search and look up your county+ free STD testing.
If you go to the health department, it is free.