It would be nice to have access to better resources and general fabricating ability.
But yea, I couldn't be a bigger fan of both modalities. Unless you have some experience with craftsmanship, I'd recommend just dropping the $300 on an econo prowler. Between the planning, purchasing of materials, fabricating, and then tinkering, I personally would've been better served just buying the real thing. It's built like a tank and except for the pads, the unit will last a very long time.
Regarding a sled, I affixed a $10 chain to a $3 hook to a free car tire. I drag that thing all over the place. Sometimes I hook the chain up to my flipping tire. That works too.