dabac

While heavy and crude-looking, there's nothing inherently wrong with a TX35. Unless damaged or seriously worn, it should work just fine. Maybe not great, but you'd have a long way to go before you can blame the derailer for holding you back.

As bike parts are much more expensive when bought piecemeal, upgradeitis can be a real costly affliction. Pretty much the only way to make make any kind of sense money-wise is to replace-with-nicer when a part is broken/worn out, but only then.

If you decide you want a new derailer for the fun of it, well that's another ballgame entirely.

well, if you insist, anything from 30 USD to 250 USD for the part alone, depending on how much engineering overkill you'd want to apply.

I'm afraid this doesn't tell us much. If it sitting at an angle to the rest of the bike when viewed from behind, then it needs fixing or possibly replacing. Can be a bent hanger, can be a bent derailer.

It it's sitting at an angle when viewed from the side - well, it's supposed to do that. And the angle will depend on what gear you're in.

Pay heed to the old saying: "if it ain't broken, don't fix it".

You can't have looked very hard then:
Park Tool on derailer adjustment
Park Tool on hanger alignment
Sheldon Brown on derailers

I think you're mixin g things up here. The high and low screws limit how far the derailer will move sideways, but aren't really used to adjust any "angle" I can think of.

There's a B-tension screw that can adjust the derailer front/rear angle and cage position a bit, if needed. It's usually not a particularly critical adjustment though.

Here: you can find the Shimano document for your derailer. Item 1 are the high/low screws. Unless you can't reach all the sprockets, or if the chain comes off the sprockets entirely, no need to touch these. And unless the derailer is resting against the correct one, you won't see any change as you turn the screws.
Item 4 is the B-tension (front/rear position) screw.

Read up on the links.

Plot your approach according to what you want. Are you just curious about how your bike works, or is it something in its performance that you're not happy with?
If the bike isn't behaving properly, are you sure it's the bike that's at fault, or is it maybe the rider who could do with some pointers on riding/shifting technique?