This plane came out of "winterized" storage in 1992 and was purchased by the current owner in 2002 (for $25,000 apparently). I'm not sure which of the upgrades were before he bought it or after except that I know it was painted before he bought it.

I believe these things have been added since the plane sold in 2002, but I'm not sure how to look at the classified ad from 2002 to know for sure.
Garmin GNC 250XL ($2800)
MX-300 Nav/Comm ($1500)
Narco AT-150 Transponder ($900)
Artex ELT (Unsure of price, I think around $1000)

This appears to be about $6000 worth of upgrades since he bought the airplane, and now the asking price is $10,000 more. What would a fair selling price be?