Amazon has refurbished PC's for under $250 and if you want you can get a warranty for $30. I bought this one for my MAME cab. I also put in a better graphics card (under $100)

https://www.amazon.com/gp/product/B01H63TWZC/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

You can get a decent refurbished office PC for under $300 on ebay or amazon. You can get down towards $100 for an i5, but $250-$300 will get you an i7 with 500GB SSD.

https://www.ebay.com/itm/HP-Compaq-Elite-8300-SFF-Core-i7-3770-3-4GHz-16GB-RAM-480GB-SSD-Win-10-Pro/184526137385?hash=item2af69d6829%3Ag%3AJFkAAOSwPKlfpz8q&LH_BIN=1

https://www.amazon.com/Dell-Optiplex-990-Certified-Refurbished/dp/B01H63TWZC/ref=sr_1_8?dchild=1&keywords=Dell+Optiplex+i7&qid=1605140735&sr=8-8