Guest houses and apartments are pretty cheap in Colombia along with everything else. You’ll probably pay around $7 a night in the big cities and maybe $4 in smaller places.
If you decide to rent then you can find apartments for around $100 a month or less for just one room in a place. Make sure you choose a reputable neighbourhood where you’re going to feel comfortable walking around at night. Colombians will be happy to tell you where they consider to be safe and where not.
Finding somewhere can be tricky though as the classifieds in the newspapers don’t offer much choice. Often the best way is just to walk around the streets looking for signs saying ‘to let’ in the windows. Failing that you can ask shopkeepers and then lengthy discussions will begin involving at least 7 neighbours who will debate your accommodation needs at great length:
“It’s not a big place…”
“But what does that matter? He’s alone and probably doesn’t have much furniture-”
“Yes – but maybe he’ll get a girlfriend and then they’ll need the space..”
“If he finds a Colombian girlfriend he’ll never leave!” Laughter all round.