Never had a muzzleloader, but have toyed with the idea of getting a Hawkens style or mountain man type gun (I don't know the proper term for these guns).
Anyway, I stumbled across a decent TC carbine with a round barrel in a pawnshop for $150.
What are they worth?
Again, I know next to nothing about muzzleloaders.

Like other objects it really is based on condition of barrel.

Black powder is rough on a barrel and many are not maintained properly.

Price it new and used and give a good inspection B4 buying.

Would that be a High Plains Sporter or New Englander? If so, those aren't Hawkens (these are all models that were made by T/C). It would help if you know the model since some are priced higher than others.

As far as terminology goes, the T/C Hawken isn't really a replica of a real Hawken. They just gave it that name because it sounds cool. None of these models are replicas of any historical gun, but for reference purposes you could lump them all into the "half-stock plains style" category.

$150 for one of these T/C guns would be a great price, if it's in good shape. If it's a rust bucket or all beat to hell, I'd keep looking. There are plenty of other used guns out there. Have you had a close look at it?

I've been following the TC prices.  There is a wide variation.  Most common used models (not in-lines) are going for $200-400. The main problem is how much corrosion is in the interior of the barrel, especially at the rear, no good way to tell.

If you have the time and the shop would allow it. there are ways to tell. Take the cap area apart and try to get a light in there, also run a patch down to the bottom and give it a good couple turns and pull it out. If there is rust, itll show up.

Get an octagonal bbl with 1" flats.  If so you could get a Green Mountain Bbl from .32 to .58 Rifled or .62 Smoothbore.

Green Mountain no longer makes drop-in barrels for T/C or other guns (I got the last one they had). The only dealer who might still have some in stock is Pecatonica River, you'll have to call and ask them. If they don't have any left, you'll have to look for a used one.

That's too bad they sure did shoot good.

Yea..Ive actually got a spare Thompson White Mountain Ocatgon Carbine barrel, new in the box w/sites. Wonder if there is a market for it.

This barrel;

The barrel in that picture is a half-round barrel.  Fowlers are like that and so were the 1803 Harper's Ferry rifle had a similar barrel.

Ah ok..That is my White Mountain Cabine Thompson Center .50 cal.