6th edition Blue book (2009) lists ASM walker values as:
100% - $315
98% - $275
90% - $205
I've seen em go higher and lower on the auction sites. A New Uberti will cost you a bit more. The AZ date code on the frame of the one you're looking at makes it a 1990 vintage.
I've never owned an ASM Walker, so cannot speak to their quality. There will be others chime in that will be able to I'm sure. ASM made some real good stuff, then they're quality kinda went to heck towards the end of their existence in 2000. Parts can be difficukt to get. I gave an early 3rd model dragoon that needed some work. After much fitting, I got some Pietta parts to work in it and it now works pretty good.
IU just noticed there is Uberti Walker listed in the for sale section for $265. That is an EXCELLENT price.
FM