How much does it cost for a dental retainer in the US? (without insurance)?

I had braces back in 1999 (when I was in high school) and I think because I didn't always put on the retainer, my teeth started to fall back to the same patterns (nothing serious but it annoys me when I look in the mirror). Now I am in school in the US and would like to get one retainer (until I go back to my country and talk to my dentist). I've heard that the dentist cost here is expensive. ( I don't think my health insurance covers dental expenses). So, anyone can share me the expense ? Oh, can I get invisalign as the retainer also ? and how much ?
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It depends on where you are and type of retainer. The simplest retainer that I make (vacuum-form), in my office costs about $100 (but you'd have to add on the cost of an exam, since we can't treat without an exam and diagnosis, about another $75) That's the San Francisco area
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