Second hand beds would not be the most hygienic and charities such as Vincent De Paul no longer accept them as people have used them to avoid paying dispoasal charges.
I bought some new beds last year and was with a family member when they got one in Arramount and was very impressed at the deal they got compared to me. It's possible to get a wooden base for around 100 euros there. I've plugged them in other threads here before because I think a good deal deserves a plug, especially a home produced one. They had a 50% sale ad on the TV last night.