I would check craigslist and not just in your area but neighboring states as well. I am just getting started and have been looking for a cart for about a month now. I live in SC and have been looking in NC, GA, FL and TN on craigslist but haven’t seen anything that I really wanted to mess with. Then 2 days ago I just happened to look in AL and someone had just put a brand new Ben’s big dog cart with all of the bells and whistles on there for $2500. It still had some of the plastic wrapping on it. The guy was selling it for a family member that had just bought it and then passed away. I jumped in the truck and drove 400 miles to get it. You just have to be patient sometimes.
The problem with e-bay is that you can’t see and put your hands on the item before purchasing it unless it is for sale in your area. I found a cart on e-bay a couple of weeks ago that was in my area. I contacted the person and then went and looked at it. It was actually in use when I looked at it.  I could not believe my eyes at how dirty and nasty that cart looked and this guy was slinging dogs off of it. I would not have bought a dog from him so I can see why he is selling it.