You can find a tandem stepdeck for reasonable price, there was one at auction here recently went for $14.5k it was older but looked clean and was a tilt deck 2 20k air axles, was easily a 30 ton trailer. Or what about on a pintle? You can find decent tandem air trailer for under $10k at auction with being allowed 37,400 on trailer axles empty trailer weights about 8000 with some pin weight you could go up to around 35,000 on it. You're going to pay more for a electric brake gooseneck and it's going to be a inferior trailer in everyway, most of them are built like garbage compared to the heavy trailers. Parts are also way more for brakes and there is no comparison to how much better air brakes stop. Here in Alberta there is no regulations for what you can tow, as long as you are not exceeding any tire or axle rating you could technically tow 100k behind a 3500 and be perfectly legal.