To do a complete resto, you're looking at $242 for new sideart and CP art, $40 for a new fly and cap kit for the monitor, $75 for new buttons, joys, CPO, $40 for t-molding, $100 for a PCB, and $25 for a new marquee. That's $522 just to restore it to factory conditions.
That's a total investment of $1022 if one pays your full asking price. I really don't think $500 is unreasonable because at $1022, that's about the cheapest factory "restored" MK1 you'll find, if that's what the buyer ended up doing. Take the one sold by Stryker28 as an example
Just my 2 cents.