Hi
Depending on how much you want to spend you can try freecycle which is great for general free stuff or, and this is what we're going to do, pop along along to Criterion Auction rooms
http://www.criterionauctions.co.uk/" onclick="window.open(this.href);return false; on Chatfield Road SW11. They often have to junk unsold pianos and they have them on sale from as little as £40.
Happy learning!
A