^^what they said...
My trailer was a decent but old popup that I got for $50 on the local craigslist. I wanted it for the frame but I figured I'd try it out since the canvas seemed ok, despite being a '74. I used it once and started stripping it out...
Then, a while later, I was offered a tandem travel trailer that had been vandalized and the owner just wanted it off his property: a "you tow it, you can have it" deal that came about through networking with friends and letting people in on what I was doing. If it's still around when I have the time and the work space, I'll probably grab it. I've got a buddy who drives a wrecker and can drag it to my place for me.

When most people (him included) look at it, they see garbage.
I see a tandem frame and appliances pretty much for free.
I figure a case of beer for the trailer and another for the tow is a pretty good deal !
I'm actively looking for a similar $50 popup for another project but there don't seem to be any in my neck of the woods at the moment...which brings me to my (very long winded) point: you'll see all kinds of deals out there when you
aren't looking for them !
Remember too that nobody is going to take the time or spend the money to post an ad for a trailer that they'll let go for next to nothing, and it doesn't cost a thing to knock on the door and ask. And if they say no, leave your number anyway because they might change their mind after ruminating on it a bit.
I paid a case of beer and $60 in dump fees for the slide-in camper from which I pulled the appliances, windows and some other bits and bobs I may or may not use. I'm going to sell the fridge since I won't be using it and I ought to be able to get $50 or $60 bucks for it since it's cleaned and working.
Like you, I'm building on something of a shoestring budget and I'm still making progress...even if it's not going as quickly as I'd like.