Need affordable prime lens

For $100, you should easily be able to get a minolta 50mm 1.4 and an adapter. I have the rainbow imaging one...got it from Amazon for $18. And I scored the minolta 50mm 1.4 for $95 on ebay. They go for around $80-$100.

I was also able to get a minolta 50mm 1.7 for $20, which is about what they sell for regularly.