I would go for it. There is so much to see in this country and you and your family should see it while you can.
Yes you can get a good, used DP for your budget if you shop carefully. I would look for a well-build higher quality rig in the years that keeps you in that price range. Some brands/models to consider are:
Country Coach
Newmar
Travel Supreme
Monaco
Beaver
Foretravel
Since you plan to do your own mechanical work, strongly suggest you shop for a side radiator coach. You will see the difference in side radiator and rear radiator when you look into the engine bay.
Good internet access is easy these days. We use a Verizon MiFi gizmo that works very well so no need to rely on often unreliable RV park WiFi systems.