You can get to Colima by plane from Mexico City or Tijuana. Aerocalifornia, Click, Mexicana, Avolar and AeroMar offer services to this city. Airport is located 15km north, outside the city. To get to the downtown your only option is a taxi, which will cost $20.00 USD.
You could also fly to Guadalajara, which is Mexico's second larger city, and where there are more flight options. From there you could take a bus (30 usd), which will take 3 hours to get to Colima bus station and from there to the down town a cab will charge you 2 or 3 US dollars.
You can sleep downtown in the Hotel Ceballos ( Best Western )or Hotel America, just out of the downtown you find the hotel Maria Isabel and at the edge of town is a Fiesta Inn.