Hi there and welcome to I've got kids!
I think, like anything, it's down to budget. I've just bought a great single bed from ebay (or our site once the 1-stop launches!).
I'm in the process of selling a gorgeous toddler bed which my daughter has grown out of. If you're interested, let me know! https://www.facebook.com/media/set/?set=a.29162650103.104886.723285103&type=3&l=7b8266c5b2
you can see pictures of it set up as a bed there.
My first point of call would be a site like ebay as you can get some great deals at affordable prices.
I hope this helps!