checking sold auctions on gunbroker is the fastest way to see comps to deal fairly with friends.. like it or not, gunbroker sees a lot of traffic and their search tools work well
must be logged in, advanced tab, completed auctions search.. keep in mind condition, age, number of mags, accessories, etc. when comparing value.. and you can compare prices of what is selling vs not
I got this xds .45 with robar treatment and 7 mags for $550 few years ago.. 8th mag courtesy of springfield when shipped back from recall.. also came with the essentials kit which is essentially useless
been an extremely reliable compact ccw with a heavy punch.. not a pleasant range toy with hst+p but still very manageable tool for the job
bought this xd 9mm in 2003 for under $400 new.. had quite a few rounds through it in 21 years of service, no failures, no complaints.. just an ordinary every day good running gun for range or duty
good luck with your deal with your friend!