For a split level 1500 square feet you would probably need a 2 ton (that would be plenty). Up to 1500 square feet we normally recommend a 1 1/2 ton but in a brand new home. What we sell a 2 ton for in canadian $ is $1500 plus tax- installed. But this is in a brand new home. In an older home or a home where the basement is finished there are other variables and usually the contractor needs to come to your home to gibe you a better general idea...
Is your furnace new or newer? This makes a difference because if your furnace is say 20 years old- it will need a "fan center"- (a part to equip it for a/c). Furnaces, depending on the brand from about 9 or 10 years and younger are already equipped for central air and don't need that part.
Is your basement finished? If so, the contractor may charge you extra and he would possibly need to cut a few holes that usually the homeowner needs to fix afterwards. If you have a t-bar ceiling it's easier but whether the basement is finished or not is a factor.
Do you have an idea of brand name? In our company's view there are a few main differences between air conditioners...having said that, if you have three brands- all same warranty, compressor and SEER rating (energy efficiency rating) you'd be surprised at how different the price is between brand A, B, and C. We sell GOODMAN beacause it offers the best overall deal(we feel). Now mind you, our customers live in Canada and in our climate we need this A/c 2 to 3 months of the year TOPS (on and off)...so we feel that it's unwise to pay a ton of extra money for something that promises to be super high efficient- when it will take 10 to 15 years to recover the cost in savings...I hope this is making sense... In your climate you may need the a/c every day of the year and then you may want to pay more for a more efficient air conditioner... Many brands of ac's are much more, not because the company is larger but because they spend a lot of money in advertising and that is built into the cost of the unit.
I hope this has been clearer than mud for you...if you have any ?'s please ask- I must go beacsue it's actually close to 75 degrees out and that's hot for us here!
Paula