I'm not up to speed on latest prices but a brand new Taiwan 9x35 BP clone goes for about 9K$ FOB your door in Calgary +GST +/- exchange. Next size up 9x49, probably +2K$? its typically same head but some brands increase the motor HP. Depending on your available shop amp duty, 'electrics' are important decision makers. Align/Taiwan brand power feeds are in the 500 range for table, 575 for knee; about 30% less for Chinese versions. DRO's vary but lots of happy customers with Chinese brands. Sometimes mills are sold as packages & accessories bundled at lower cost and pre-installed. Kurt DX6 crossover is ~$635, the 6" versatile ~$965.
https://www.kbctools.com/catsearch/352/milling-machine-vises
Guys on the forum know better than me but usually if everything is in nice shape your should be able to apply a factor like say 60% times new. If its old, outdated, issues... price goes down. But there are always exceptions.
Calgary / Edmonton reference
http://www.moderntool.com/products/category/milling-machines-new/
BC reference
https://www.kbctools.com/CatSearch/1540/manual-knee-mills