I've always understood pro line to be what a number of manufacturers in the 90s (Reebok, Nike, Starter...) referred to as their retail authentic range.
Champion is one of the few brands of authentic that I've never owned, but I do know they changed the tagging a lot in the early 90s, so it's pretty difficult to know exactly what type of jersey you're looking at based on the size (i.e. some gamers used "M", "L" etc. as the sizes, whereas others used numbering.) They did have some unique jock tags between around 94-96 that made gamers easy to spot, as they were dual-tagged. There's a Bills example of team issued Champion jersey on eBay if you search number - 230634618092.
In terms of value, as always it depends on player / team etc. But I'm not aware of the retail authentic range being overly sought after or valuable. I can't say I've heard Champion mentioned when people discuss their favourite era of jersey in terms of quality etc. either.
I will look to get a Bills team issued Champion similiar to the listing above at some stage, but wouldn't pay close to what that seller is looking to get for it.