Not GP, but I moved to Costa Rica for a few months in 2013.
Depending where you go, you can get away with very little to no English.
I was in a (tiny) surfing town, Playa Grande. It gets a lot of foreign surfers, and so all the locals speak English. Many ex-pats live there year-round. Nearby is Tamarindo, very similar there, and a much bigger town.
I can order food and ask for directions and have basic conversations in spanish, if they slow down for me--but I found speaking spanish was always just for fun, and virtually never a necessity.
The owners live a few steps away in their own home. The wife cleans your place once per week. The man will taxi you around as-needed (he charges normal rates, which are pretty high there--gas is expensive). They are FANTASTIC people, they made my stay much better than it might have been.
There's a wall around the property and a gate that gets locked at night, but in all honesty, I've never felt safer anywhere in my life than I did in Playa Grande--wall or no wall.
Edit: I paid $550/month for that place in the off-season. The prices listed seem a little high, they were going to charge me $600/month in season (US winter is their season, US summer is their winter, and it's pretty rainy).
Depending where you go, you can get away with very little to no English.
I was in a (tiny) surfing town, Playa Grande. It gets a lot of foreign surfers, and so all the locals speak English. Many ex-pats live there year-round. Nearby is Tamarindo, very similar there, and a much bigger town.
I can order food and ask for directions and have basic conversations in spanish, if they slow down for me--but I found speaking spanish was always just for fun, and virtually never a necessity.