The Finn rifles are much better quality and correspondingly higher price. You should be able to find M95, Dragoon, M91/30, M39 all pretty affordable for excellent examples. M27s & M28s turn up now and then for usually a lot more money unless the seller is a complete ignoramus.
The surplus ammo is all corrosive. Clean as normal then flush the bolt, chamber and barrel with a generous amount of plain old water to dissolve the potassium chloride (KCl) then dry and oil. Potassium chloride is hygroscopic and will collect water which rusts your barrel but it is the water that does the work of removing it, not the stink of the ammonia nor the pretty blue dye in Windex. It really doesn't take a lot of water, a few ounces is adequate as long as it wets the surface and runs out enough to remove the salts.