using an ac unit or buying/making ice to chill the beer will all cost money, the best option would be to create a well insulated fermentation chamber/ room
once the ac unit gets the room to temp, it should loose little cold and cost very little to maintain
I just dip my mason jars in star san prior to filling with yeast, I have reused the same yeast now over 7 times with no bad signs from lack of sanitation
here's a simple and fairly cheap recipe, obviously if you do it all grain it will be cheaper
3lb bag of extra light dme
3lbs of table sugar
add hops to bitter in boil ~20ibus
dry hop with an ounce or 2 of cascade
just make sure you control fermentation temperature for the first couple days...
first there is a huge thread on here about no chill
I've only done no chill a couple times, I usually use my immersion chiller, but that's only to save time.
regarding infection your whole boil kettle has been sanitized from boiling and so will the lid, I've even had leaves fall in my beer...
happened to me a couple weeks ago, I decided to no chill the batch, worked great, maybe a little more bitter than it should have ended up, but was still very good