There are a few factors to consider beyond what you listed. Size of the Space, what already exists in the form of floor (Garage floors are not level, they are poured at a slight ramp, toward the garage door, so water will flow out of the garage), Framing *stud work* (What exists may not meet current code for living spaces (16 inches on center) and may need to be adjusted or completely removed and replaced), how you want to deal with the garage door, if the garage is attached or detached, how much electrical already exists in the space and what the building codes and housing codes are like in your area. Then there is usually Hidden factors, a bit of damage that is uncovered in the construction, a crack in the foundation, a bit of termite damage - a bit of rot, nearly always one finds those sorts of things in remodels. Some areas demand that you have a garage. With a garage door. The "around" on that is to leave the garage door and to build a "false wall" or partition in front of the door. Thus later down the road the garage can be a garage again. Since many garages act as mechanical room as well (furnace, hot water heater, electrical panel, blah) Many places have strict codes on the usage of the "garage" area and insist that new venting and even moving these mechanicals take pace before the garage can be turned into a living space. Building and Fire codes play a huge roll in this. In some places the building code is silent, but the fire safety codes take over and act as "part of" the building codes. For the USA there is no one single set of Codes that apply nationally. They are "working" on that. Your best bet is to find at least 3 general contractors in your area. Have them give you an estimate. Walk around with them and let each one of them tell you what would need to be done in order to meet code. Handymen (Unfortunately) have gotten a bad rap in more recent years. Most handymen are "good guys" who are honest, have studied building code and know what they are doing. Sadly there are too many who know nothing, abuse the client, or rip the client off. There is a "safe" way to use contractors and handymen to do these sorts of jobs. In many places "lay people" are allowed to do some of the work. Like pulling wire, hanging electrical boxes, hanging dry wall, as long as there is an expert who can check over their work before the inspector comes out. Thus you can hire "handy-people" to do the labor under the guidance of your contractor. it is usually "cheaper" this way for the labor. Another consideration is how and where you order your materials. A single 2x4 can range from 1.87 to 2.50 in the same area depending on where you go (Around here) that may not seem like much of a difference, until you are purchasing 10 or 20 of them. That .63 difference can add up to $6.30 or $12.60 maybe still "small" but when you consider that dry wall has ranges, insulation, wiring, fixtures, etc, etc, etc, it can add up to the hundreds of dollars in most renovations. Minor things like what you use on the floor can have a huge impact on your budget. If you use Italian Marble (the real stuff) over Ceramic Faux Italian Marble, the difference can, for your average garage space - be measures in the thousands. The reason why they price in the Square Foot is not to make it easier for you to calculate the over all cost, its to hide the huge cost that doing an average room would run. The consumer "thinks" that $2.30 a square foot sounds good - until they realize that their space is 18 X 24 or 432 square feet (993.60 BEFORE taxes and installation costs). When it comes to space heating/cooling one needs to think in the long term. Many "cheap" space heating methods may seem like a great price on the shelf. Long term considering power/fuel usage the "cheapness" is driven home while your wallet is devoured in energy costs. More so today considering how fuel and energy prices are going through the roof. When you do get an estimate, expect a bit of delay between the visit and when you get the estimate. If the person is throwing out a number right on the spot then you should proceed with caution. A "good" estimate should take a bit of time to calculate. Estimated hours, estimated materials, special considerations of the space may be 'roughed out' however a calculator should be used and measurements taken. So you could "invest" at a high price for a highly fuel efficient space heating system and not see a "return" on that investment for a few years. Or you could go cheap and end up paying much more in the long run.