What are the different ways to get to Yaxchilan from Palenque?
There might be a way to get there without taking the boat, but I think most, if not all, tourists reach the site via the boat from Frontera Corazal.
I know I have seen someone here mention to take a tour from Palenque (combi, then boat ride down river - all day trip)
This seems to be a good way to do it and could be less expensive than going on your own.
Is it possible to drive to Frontera Corazal and take a boat ride from there?
Yes, this is what I did, though I took one of the public transportation vans down, rather than driving my own vehicle. I was dropped off at the turnoff for Frontera Corazal and hitch hiked into town from there (the van I took continued south on the highway). There was a taxi waiting at the turnoff, but it was easy and free to hitch hike instead.
How much would it cost?
I've read that there are tours from Palenque for around 600 pesos. I got down to Frontera Corazal for around 80 pesos, but the boats cost 1200 pesos per trip, with two hours of waiting time at Yaxchilan. I spent a night in Frontera Corazal and was lucky to find a group the next morning that were going to the ruins and I paid 250 pesos to join their boat. Otherwise, I would have paid 1200 as there were no other people going at the time.
Needs to be reserved in advance or just show up to FC?
Just show up.
How is the drive and road from Palenque to Frontera Corazal?
Good paved road all the way.