my very loose back of the bar napkin maths put it at 10~12K if you were very selective, fortunate with parts and patient-- waiting for deals, using 2nd hand parts and shopping judiciously.
of course you could just open up a catalog and melt a CC and be at 20 easy money
(cue everybody saying it can be done for 10 bucks and burrito with money left over for a 12 pack)