If your extension cord gets tangled up, don't pull on the ends. Instead, gently loosen all the tighter snarls in the middle until them become larger loops that can easily be untangled. A way to avoid tangles is to use a retractable cord reel. It will let you reel out only the amount of cord you need, then quickly reel it back when you're done.
Shop during the off-season. Many heating and cooling manufacturers offer significant rebates during seasonal sales promotions, and dealers may charge less for installation.