If you are switching, you'll need a house valuation. If you are moving within the same bank to an LTV mortgage, you'll also need a house valuation. Banks have a roll of valuers that they accept to give valuations. Your income won't affect the switching question if the house is in negative equity (but will, obviously, for mortgage approval).
You'll have to spend the €150 to get a valuation if you want to switch banks or switch to an LTV mortgage with your existing bank. That said, I had that exercise done last summer and the bank's valuer valued the house at a staggering €410k when two local estate agents (at the same time) ranged from €320-€375k so you may be pleasantly surprised with the bank's valuation (so long as you don't care that it's not based in reality!)