With Oblivion and Morrowind having sale prices, could anyone tell me whether the level caps in their expansions are raised from the core games and to what numbers?
Look for the unofficial elder scrolls wiki online, where you can get more info on that.
I've recently played through both, but I exploited Morrowind a lot, so I can't quite tell for it.
As for Oblivion, as stated by dtgreene, max level depends on initial class and you can carefully grind your level to max the stats while maxing the skills (except for luck witch doesn't have a skill that can multiply it). Players that want more control over the evolution of their characters may end up going for classes that don't reflect their play style at all.
When you're high level enough that all item drops became available, you'll want to go for an specific item build that makes you almost invincible and able to kill anything very very quickly. Refer to the unofficial elder scrolls wiki online to learn which items you should look for and how to best combine them for said effect.
As for me, I did give up on trying to max my level because I had finished all major story lines and the remaining skills to max out were extremely grindy. I also gave up on getting the final amulet I needed for the completely invulnerable build (in a way that only arrows would be able to damage me) because I was already nigh unstoppable by all accounts and the damned thing just wasn't dropping.
EDIT: On a side note, seeing the amount and variety of exploits in Morrowind (some of which can break the game for you) and the grindy aspect of leveling in Oblivion (which I'm sure is very much the same in Morrowind), I finally understood why Skyrim simplified everything, and playing through Skyrim and going for the max level as well (though I didn't rely on making skills legendary) made me understand why they simplified things even more for Fallout 4. Grinding and carefully building stats is fun for some people (even me to a certain extent), but they severely hamper game play and exploration.