OK here are the "insider tips" from somebody who lives here in La Fortuna:
Lodging: Bueno-Bonito-Barato or Chillout Backpackers
Activities: Walk to El Salto & go swimming with the locals and use the tarzan swing, Tabacon free hot springs OR for $9 go to Los Laureles Hot Springs (across form Hotel Los Lagos-you can bring your own food & drink and there are tables, shelters, lock-boxes and BBQs), Lands in Love tour has white water river rafting, zip lining and more...a full day of adventure at an unbelievably cheap price, Red Lava has a volcano hike, stops at the free Tabacon hot springs & more (I don't sell tours so I'm not 100% sure about all that it includes but I know it's CHEAP)! :-)
Cheap eats: #1 Grocery Store (can't beat that) or Soda Hormigas-by the Mega Super Grocery Store & Bus Station
Alcohol: Stop at the Duty Free on your way into Costa Rica if you want wine or alcohol. Beers can be purchased at a liquor store in town (Licorera in Fortuna-good one-is 1 block from bus station-take a left at Importadora Monge)-pay cash and get an even better deal.
Check out the FortunaSocialClub.com and see what they're doing that week you're in town-there's a happy hour every Thursday and the prices are always good!