I am not an expert, but just a DIY guy, who has layed some wood and tile flooring myself a few times. Here are some of my thoughts. In your first paragraph you said you wanted to get an idea of the cost to extend the wood...well regarding that thought, I would hestitate to replace the carpet with wood if you were trying to make it match the existing wood. I think making it match would be next to impossible, unless you sanded it all, and then restained/refinished it all or if you could find wood that was a good match as far as color and grain patterns. Even if you could find something that "matched" (color/grain), it might still look visually unmatched after it is layed.

So if you don't put in wood that is attempting to match the existing, then I think it needs to be obviously different. Different in color and contrasting dark/light shades. I personally think that whether it is cork or wood, as long as it obvious that you are "not" trying to make it match, then I think it would be fine. Such as if you were trying to find something to go with a traditional golden colored, oak flooring, I think a blond wood like natural maple or natural hickory would look good, or something darker like a chocolate color. Cork might actually look better (in a contrasting color), since it would be obvious that you were not trying to match the existing wood, in the same way carpet is obviously not trying to match the wood. Might also consider tile, I've seen some nice tile/wood combo floors before.

But I would need to reserve final judgement until I had some samples in my hands to hold next to the existing flooring, to see what it looks like. There are many online flooring stores that provide free or close to free samples.

As far as your height differences, one thing I've read is that cork flooring needs a level subfloor just as much or more as regular wood flooring. Beyond that, I'm not the best guy to advise on this.

Those are good thoughts. We presently have a transition strip of flooring where the wood meets the carpet. It's a board that goes the opposite way of all the others. The floor person said we had a couple of choices and one of them was to keep that transition instead of trying to weave in new flooring. He said we could dress it up to look more like a premeditated border between spaces (foyer/living room and kitchen/dining room) by adding a second strip or even create a border around the rooms. He said that the added benefit was that the stain match wouldn't have to be perfect and also that if any part of the floor had to be refinished, the transitions would be a natural stopping point and you wouldn't have to refinish the whole floor at once.

I got the estimates in an email last night and with the cost of cork vs. the cost of wood, I think we will go with wood, but because of this goofy subfloor (it's 3 1/4" pine tongue and groove planks running perpendicular to the joists - porch flooring, he called it), things may get complicated and more costly in the attempt to get a level subfloor.

Knowing the wood may be quite pricey, we're going to wait and see what our year end finances look like before we move forward.