How to have donation based, name your price digital products

Site URL: https://join.oraclegirl.org/product/karmic-delete-6-2-source-connection-recalibration-mp3/

I'm wanting to have donation based pricing on my website for digital products. Is there a third party payment processor that would do this and how would i integrate that onto my site? I've left an example of exactly how I'd like it to work. Someone can name their price, yet a minimum donation amount is in place. 

Thanks :)