If you learned classic skiing as a child I think that is a good alternative. If, like me you were no good at it in childhood skating is a much better alternative. It is very difficult to get a decent grip on classic skiing as an adult. Skating on the other hand is a bit easier. I was passed by only two skiiers today (and there were a lot others out there) One was a classic skiing gold Kayak medallist olympier (Knut Holman) and the other a better skater than me. We cyclists can use our quads skating and with a decent Vo2 uptake it is both fun and possible to go quite fast. Another advantage is that you just have to have a couple of gliders, and not a whole bag with different stuff to put under your skis. Buy a decent quality set off Ebay or if you have the money buy good quality new stuff. Especially get good poles. Try it, it is a great complement to bicycling. My weekends now are one day cycling and one day skating.
I'm a beginner at both. I'm finding that skate is much more intense - I can barely regulate my HR - either i'm standing still or at 95% max. Classics are much easier to go at a moderate rate. I've been skating for 1-2 hours (until I'm dead) and then I can classic for another couple hours after that.
You should definitely find out how hilly your local ski area is - if it's really hilly (mine is) skate is really really hard as a beginner. Classic is easier for hills - and you get plenty of workout.
My friend races both skate & bike, and trains separately for both. I think the real benefit is keeping your cardio up during the snow season, as opposed to actually building muscles that work for both. Someone please correct me if i'm wrong here.
Sorry to not answer your actual question.
And -1000 about Craigslist for skate skis - I would go to a real nordic store to get a recommendation, there's this complicated "flex" thing, and I think you can really make a lot of mistakes with your gear if you don't get some help the first time. It's not as simple as weight/height.
I race both styles. Skate will work the biking muscles more, but in reality, neither really builds muscles for biking. Both build core strength, and will require that you build core strength. You need to get fitted at a reputable nordic store. Find a good nordic ski store and get yourself fitted for a pair of skis.
i started classic about 3 years ago and it's a great workout. rather lucky to have property in the area of the birkie trail in northern wisconsin. the same place i ride bikes in the summer. i believe the most important part of the experance is to get fitted at a good ski shop. my neighbor bought skiies used on the internet and has been complaining ever since.
just my 2 cents
I am new and I completely agree with this "I'm finding that skate is much more intense - I can barely regulate my HR - either i'm standing still or at 95% max." It's non stop pain. Awesome for your core, and your cardiovascular system.