it seems like if i capture a planet that has corruption it will removed slowly automatically without having to pay the $2000, is that normal

yeah it' is normal to remove corruption when you take a planet .removing corruption in this mod is a pain but just find all the heros that don't have there own special ship in space then just try to remove corruption because this mod adds alot of heros that can for each faction remeber to keep them as a single unit fleet when moving using there removal power as it doesn't work if there with other units.
here's a list of soem i do know for each faction
Empire
Palpatine, tarkin, another hero that spawns on coruscant and another hero on sullust
Rebellion mon moffma jedi heros like luke can but you need to take tatooine for him i think leia can

2000 credits to remove corruption on your own planets is way too expensive

you can leave the corruption as all it does is allow the pirates the ability to pass by your space fleet without triggering a space battle but if you're stuck for cash u should focus on getting a money planet or limit where you're defending to make choke points to defend and get strong ships like capital ships or cruisers as they can tank hits

Do not ignore corruption, not only do they get money out of it but unlike the rebels they can move everything and the kitchen sink without being intercepted through corrupted space. Unless you wanna lose stations and planets behind the front to capital ships always take care of it. Eventually they will run out of agents and will slow down on the corruption. You'll still have to keep an eye for it and you will have to clear it once every 2 weeks.

Place heroes that can remove corruption on the places they corrupt repetitively, it's usually going to be the border with the BSun so make sure you don't let them surround you.

For the rebels: Leia, Mon Mothma, Kenobi, Kyle Katarn, Lando, Organa will clear corruption (probably Yoda as well). Iblis text says he should but he doesn't in 2.6

Pro tip, as the empire I like to allow corruption to spread to a coupld of key planets such as bilbringi/Kuat.
After that, I remove the corruption on every planet EXCEPT those key planets (and other shipyard planets)
The corruption gives a signifigant discount which is vital for shipbuilding. Also, if you remove the corruption on all the other planets then it removes their ability to move troops etc. basically, all the benifit with 0 risk.

Doesn't corruption also increase build times?

Originally posted by Palora McWhine A Lot:

Doesn't corruption also increase build times?

I honestly do no know, but in my opinion the cost is a bigger issue. Until late game, where you can make close to like 60-100k the cost of the capital ships is going to be the only thing really preventing you from expanding. The corruption also lowers the prices of the shipyards themselves.
If you really cant handle construction times then simply start a build que with the reduced prices then remove the corruption.