Not sure exactly what your question is exactly.
Used RV gensets that have come out of wrecked or parted out RV's can be had all the time for less than $500.00. Most will be large enough to power up an A/C unit.
New gensets that are large enough to run an A/C unit will start about $500.00 and go up from there.
Roof top RV A/C units can be purchased for $500.00-$1,000.00.
Window or portable A/C units can be purchased for $100.00-$500.00.
Split A/C units can be purchase for as little as $700.00.