Let me first qualify what I will say by admitting that sometimes people find a special deal and get a great boat for a cheap
price. It could happen to you but you also might win the lottery and $1,000,000 prize. The point being, the odds of getting a super cheap deal on a really good boat are very, very small.
For €50,000 it would be very, very lucky to find a good quality 40-45' boat in good condition and with good equipment
for cruising. 35' or so, maybe.
You should be prepared to find a boat that needs work and be prepared to do the work yourself.
Also, have you considered the work and cost to maintain the boat? Buying
the boat is just the beginning. What are your skills? If you have to pay a professional to do the repairs
you could easily spend more than the cost of the boat in repair costs.