That would depend on a lot of things, I'd imagine. First, your sense of upkeep with your vehicle. If your vehicles are well maintained, why not? Second, your sense of adventure. If your vehicles are well maintained, and you know you could have a breakdown in your driveway, 5 minutes from your house, at work, or across the country, and you don't mind a delay for a repair, why not? Third, your willingness to take a membership in a roadside assistance plan, such as AAA, Good Sam Travel, etc., and count on them to get you towed (if needed), and a decent mechanic worth his salt who won't take you...why not?I wouldn't feel comfortable driving an older vehicle across the country like that. The peace of mind alone might be worth it to rent a car.
Finally, for us, it's faith. Our last 3 trips have been taken in older vehicles with more than 100K on them, out of warranty. On the 2011 trip, our worst problem was a couple of burnt out safety lights. On the 2012 trip, we had a little "oopsy", then an alternator that was "going south". Easily repaired, and faith and prayer (we believe) got us to the city where it could be repaired without issue. On our 2014 trip, we had a problem that is still not completely solved, though we know now we won't need a new fuel-filter/water separator for awhile, or a #8 injector, or one other part. Yet we will take that same vehicle on our 2016 trip.
I've never used Priceline, but we did use hotels.com a couple of times. Just do yourself a favor before hitting ACCEPT on a "deal" from there or Priceline....go to Google, TripAdvisor, or whatever ratings place you like, and check it out FIRST. One place we took on a Hotels.com deal, gave us a hotel which was smelly, and very rundown. We didn't look at the TripAdv reviews first, and for that, I blame myself. Another time, my daughter and her family took a "deal" which said "5 minute walk to Disneyland". It was more like 15 minutes at the fastest pace. My son-in-law said that if he'd read the reviews FIRST, he'd have found that out.