I need temperature control for my garage for my tarantulas

My tarantula addiction started when I picked up a cute little rose hair tarantula from the pet store on a whim.

Now I have over 70 pet tarantulas.

I also have a list of at least 70 more tarantulas that I would like to add to my collection. I’ve decided to convert my garage into a tarantula room but the garage does not have any HVAC ductwork or vents in it. This makes sense, of course, because cars and storage items generally don’t need heating & air. However, my tarantulas do. I’ve called a few different heating and air conditioning companies for quotes to extend my existing ductwork into the garage but the HVAC technician who come over tell me that I need to get a bigger HVAC system to handle the additional space. I really don’t want to do that. That would cost a lot of money and I don’t have thousands of dollars to spend on this project. After all, any money spent on the HVAC system, is money I don’t have to spend on acquiring more tarantulas. One HVAC company suggested that I get a separate HVAC system for my garage. I was about to dismiss this until he suggested simply getting a ductless mini-split system or a window air conditioner with a floor heater. That got me to thinking. I’ve looked into both options and I’m really not sure which is better at this point. But I do agree that it makes more sense to just get a separate heating and cooling system for my garage rather than get a huge new system for my whole house. It should cost me less anyhow.
Air conditioning filter