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Thanks for the replies @Glws and @LeMesjeu,
As you guys gave different answers I figured that it doesn't really matter what crank to get.
I managed to find a rotor crank for 80 euros second hand. I'd say the chainrings are still in good condition. I'll clean up the crank and post some pictures later.
The only doubt I have about my purchase is that I kept BB30. Bearings are steel, and a BB30 axle is aluminium, this apparently causes galvanic corrosion, causing the aluminium axle to gall. I'll be sure to regularly grease the interface between the bearing and the axle to prevent that.
If the axle really starts degrading and I start feeling slop in the crank, I'll just buy another one.
EliasV-
the problem is not really the interface between bearings and axle, which needs greasing and moves a bit so is unlikely to seize if you use your bike.
The common reported problem with bb30 is the interface between frame shell and bearings.. where similar small movement can cause creaking. There is varied feedback on the internet about that, some will say no problem, some will say nightmare, and one person's experience might not apply to yours. Threaded adaptors have had good results for many in case of issues. -
I have used loctite 234 on the bearing and frame interface. Shimano premium grease on axle and bearing interface, bb30 bearing shields and axle splines. Have had zero issues on creak.
I usually do a big maintenenace run before and after winter, cleaning and regreasing. Replaced bearings after about 15k km but it was all pretty hassle free.
Glws
LeMesjeu
The only correct answer is a SI crankset, you should be able to find them for less than €250 secondhand. here and here
If you do decide to go for SI cranks, I have a set of BB30 bearings, circlips and shims sitting in my parts bin you can have for shipping. (suggesting you are stating euro prices, it will not be too far from me)