Where in CR are you headed?
Roosters are in shore fish so you can use a smaller boat (less $),,,, but while not impossible, they are tough to catch on fly.
Jan is prime sailfish time in central and southern CR,,, Jaco, Quepos and the Osa Peninsula. A good offshore charter is going to run $1000 or more, but if you really want to get a sail on the fly that is what you have to ante up to get a good crew that is capable of teasing the fish to the boat. A lot of the cheaper crews will tell they are expert at flyfishing but all they do is simply troll the flies.
I can personally recommend these guys.
http://www.bigeyecharters.com/ We caught 9 sails on the fly in two days with Ross at the helm and Frankie as first mate.
I have used cheaper charters and literally have been "taken for a ride".
A sail could be caught on good stiff 11 wt, but a 12 -14 wt would be easier on you and the fish. I caught my sails on a TFO LD bluewater which can be had for around $300 (great tarpon and shark rod too).