how to remove oil from mtb disk brake at home
I use Carplan Brake and Parts Cleaner, purchased from my local auto parts shop. This contains about 30% IPA (isopropanol) and 70% Naptha.

If you don't have many bikes, it may be easier to visit your local car mechanics' workshop and ask to use a little of theirs.

If you have contaminated the rotor, you will also have contaminated pads. There is a procedure to restore pads using brake cleaner, an oven and a blowtorch... This isn't worth the effort and risk, so buy new pads.

You don't have to buy your caliper manufacturer's own pads, so long as they're the right shape; I've had no problems using Clarks and Ashima pads.