I towed my 71 bus about 200 miles from near Coalinga to SF. I rented a 7.3
litre Diesel UHaul  and a tow dolly for around $150 plus gas. The truck got
better than 15 mpg. So I'd imagine 600 miles would be pricey! My rental was
one way. Towing is really hard on a transmission. Maybe somebody near your
destination can rent you his or her own truck and you can get a tow dolly
from Uhaul. Otherwise it's easy and not dangerous. Just be sure to make sure
your wheel is unlocked. Disconnect the battery. 
Good Luck!