You can't change barrels on a Venture without the aid of a gunsmith or gun smithing tools. If you want to change barrels get the Savage it is easy to do. I'm sorry but I think T/C Dimension is one abortion of a rifle and wouldn't spend my money on it. If it were my choice I'd plan on buying two T/C Ventures or buy the M12 in .22-250 and use a different chamber than the .25-06 for my second barrel.
The next problem you have with wanting a .22-250 and .25-06 is that the .25-06 will require a long action if you go with the Savage and you are looking at a short you'll need a three digit action like 112 to make it work. However you could run into problems feeding such a short cartridge out of the long .25-06 magazine. The T/C Dimension is a long action regardless of cartridge. So for the two cartridge choices you want the Dimension would be the easiest with two barrels and two properly sized magazines, but probably not the cheapest since you only have one source for barrels.
Pretty much every single barrel maker out there offers Savage pre-fit barrels. You can pick up barrels for $100-500 new all depending on what you want to spend. All you need to change out the barrel on a Savage is a barrel nut wrench, a set of GO/NO-GO gages, and a way to hold either the barrel or action while using the barrel nut wrench. It sure isn't rocket science to change out a barrel, and there are plenty of instructions on how to do it properly around the web.
If you want a similar cartridge to the .25-06 but on a short action if you buy the model 12 you'll need to go with something like the .243 Win. I own both the .25-06 Rem and .243 Win and can tell you that animals shot with either can't tell the difference. I've taken pronghorn, deer, and coyotes with both and they are just as dead when the day is done. I like my .25-06, but if I was running one rifle with two barrels I'd pick it to run on the same length of action but I'd skip the .22-250 and run a .243 Win and a .308 Win or larger. The reason being if you hand load you can replace the .25-06 and .22-250 with the .243 Win by running 55-100 grain bullets. Then you have a larger cartridge like the .308 to take game larger than deer if you ever got to go after animals like elk and moose.
Sorry for the long winded reply.