If you’re handy with a few simple tools, replacing the boiler sounds like a good option. Certainly, try to clean it first, but replacement isn’t a tough job either. Read the guides on Ifixit, and search on youtube videos. Parts are pretty common on Ebay, sometimes you can buy a machine just for parts pretty cheap. Just chop shop out a boiler and reinstall it.
Sometimes you get REALLY lucky. I bought a brand new Starbucks Barista SN006, in the box, for $150. I almost fainted when I saw it. Now my old one is is slowly but surely being repaired and cleaned, and my wife isn’t bugging me to fix it!