When I moved to El Salvador, my first major concern or thought (after surviving) was if I could get internet access. Why?
Communication with family, free calls back to the USA using SIP (MagicJack), Movies/Television, News and now even work.
So I was very concerned, I had heard yes, but had no idea as to the coverage area, price, how fast it was.
The good news is that El Salvador has very good coverage, internet is practically available everywhere, high speed, I've yet to find an area where it is not, and we live quite a ways away from the capital, etc.
The internet comes from several companies, to name a few: Digicel, Tigo, Claro.
I personally have experience with Claro. It's ADSL. It's fast, rarely goes out.
The price is good by US standards but a bit steep in El Salvador.
The usual price range is based on speed and goes 256k,512k,1MB,2MB.
1MB is about average DSL in the US, that will run about 35 dollars a month in El Salvador, the lowest: 256k will run about 18 a month.
You can get both DSL and wireless using the cell networks, sadly 3G cell coverage is limited outside of the San Salvador area so DSL may be your best bet, although not for everyone. Claro offers non-contract internet with decent pricing.
You can also find internet access spread widely through almost every area via Internet Cafes which have high speed.
So yes, you will be connected.