I won a pram on eBay for £25. It has the carrycot pram which detaches and you can clip on the seat to make like a push chair. My intention was to put my old 14 1/2 yr westie in it as he can't walk far but always wants to come out. When I went to collect I was amazed, it was so clean and new looking, a lovely pram and I just can't bring myself to put him in it! So its sat in my garage all covered up and no use!
My husband thought I was totally mad but it was far cheaper than a proper doggy pram ......except I don't use it.
If you go for a child's pram, pick an old tatty one.