The shops around here are asking right around $700 for like nw to very nice condition plastic-stocked 10" .221 XPs.
If you get into the newer wood stocked variants with longer barrels (like 14" .223 or 6x47) then the price jumps up to around the $1000 mark. The XP100Rs will go for well over a grand but I haven't seen any on the shelves for quite a while up here.
These are retail prices in the shops. I haven't seen an XP come up privately around here for 8-10 years or so...plastic 10" for $400.
That seems to be pretty much what you've got noted for prices.
Since it's a .221 rechamber job, I'm assuming it's a 10"?
If so, that's a pretty stumpy barrel for efficient use of the .223 case but since it's a viable cartridge I wouldnt' think the rechamber job would affect the value much at all.
It might even increase the value a bit if you decide to resell in the future since .223 is still a lot easier to find than .221.
If you did the work, then you know the quality of the job.