I got back a couple of weeks ago. I ended up renting(Honda 250) in Jaco and doing day trips. The only time I was alittle concerned was when I was following a big truck hauling rocks. (I thought I was on the main road but it turned out to be a gravel pit) The water crossing was deep and the current fairly strong.
There are basically no signs once you get off the big roads, leave plenty of time to get lost
How many nights you going to camp? I spent alot of money when I was near the beach but inland wasn't too bad.