There are a few kinds of outfits that will work with plastic mountaineering boots, like the one discussed in
this thread here. The equipment discussed here is really primitive; some Silvretta AT bindings (the 404 and the 500, I think) will also work with plastic mountain boots, and they'll ski better. An ideal ski for this sort of application is something around 100 mm at the tip and 70-80 at the waist with a waxless base, but there are lots of possible variations.
Alternately, you can go with a lighter outfit and an NNN-BC system binding; here you'd be looking for full metal edged skis up to around 75 mm at the tip, probably around 60 at the waist. I've found the NNN-BC boots do OK in snowshoe bindings. Really, the best outfits for this type of skiing involve 3-pin boots and bindings, but those types of boots often don't play well with snowshoe bindings, and even less well with crampons. Again, most people will want a waxless fishscale base.
Price is highly variable. I built my waxable Karhu military ski / Fritschi binding outfit for around 90 bucks, but that's exceptionally cheap. For a solid BC nordic outfit built from the ground up with new gear at retail you should probably assume $400-700 depending on what exactly you decide you're getting.
Once you're passingly competent on the gear, it can save you a lot of time and turn what might otherwise be a tedious trudge into something much more enjoyable and aesthetic. On the right route with the right conditions, they can really shine. When I hiked Allen Mountain in the ADK's, sort of legendary among 46ers as a quintessential long day's slog, comparable perhaps to Owl's Head with changes in the particulars, I did the last 5.5 miles out in under an hour, grinning like a fool.