For your “plan”, living in a camper trailer for a couple years is a good option. You won’t have many additional costs other than the purchase of a trailer and normal utility fees.
Your capital costs for developing the site are part of the cost to build your cabin, save for a small amount for a RV pad and possibly a more convienent water/sewer/power hookup.
$15k will get you a nice used trailer that if taken care of will have a decent residual value when you’re done with it.
Laundry? Presuming you don’t get one fancy enough with a washer/dryer, you’re in the SE. A little shed/ laundry room would work.
Consider what types of work you could reasonably self perform to help stay within your budget.
