I have a 50mm 1.7, the single most common rokkor in existence, that had fungus in it. I got it with a few other things all bundled together, and didn't need it, so it didn't matter if I screwed it up. So I took it apart and cleaned it, which actually worked very well and took maybe 15 minutes. If you have tiny screwdrivers (like a 0 or 00 phillips), that's pretty much the whole battle. Depending on whether you want to go in the front or the back, you'd also need a smallish flathead to turn the plastic conical shaped piece that holds the front elements in.
But if this is a 50mm 1.4 or 1.2, or a 58, or a 24, or an 85, etc... probably worth paying someone.