I have found that online you can either book bog-standard hostels with dorm rooms for cheap, under $20,000 per night depending on the city, or more luxurious or multi-national hotels which are more expensive from around $170,000 per night for a private room. There is a big price gap online but once you arrive somewhere and ask around, you will often find independent hotels with private rooms that simply don’t advertise online as they serve Colombians rather than international tourists and often you can negotiate the price down to around $60.000 per night upwards for a double room.
A bus from Cali-Medellín or Bogota for example would cost around $30,000-$40,000 each way but this takes a long time which people working here often don't have and tend to travel on bank holiday weekends. Thankfully for air travel, Viva Colombia, the new “budget” airline, offers an alternative to the other companies. Nevertheless, relatively speaking it is still expensive compared to, say, Easyjet with a flight Cali-Bogotá starting from $80,000 each way if booked well in advance. But, again, this is due to the newer tourist industry and hopefully prices will begin to decrease.
I will follow this post with location-specific information regarding what to do, where to stay and how to get a good deal on the Caribbean coast and around Cali.