Well, without knowing what you're paying for your electricity (it's different in different places, and in the same place depending on who you sign up with) it's impossible to say how much you pay for electricity! When I was about 15 or 16 I had a school assignment to estimate the amount of electricity my home used. I checked the wattage of literally every electrical appliance in the house, estimated the number of hours per month they were active, checked the electricity bill, and amazingly I was only about 3% off. It would be a little more difficult these days (back then most homes didn't even have a single computer in them, things were a lot simpler, and electricity was charged at a much more consistent rate). If you're interested in getting a handle on how much it costs to run electrical items it might be an interesting thing to do. You'll be an adult soon enough and paying your own electricity bills, and if you understand how it all works you'll be doing better than most people
If you're going to be keeping animals, especially reptiles, get yourself a tape measure and become familiar with lengths/physical dimensions. It's pretty important and very easy. I'd have thought they'd be teaching you about that at school. I suppose any holes in the education system these days shouldn't surprise me, but it's worth being familiar with this for your own sake.
Correct, different materials can change the nature of the basking spot but probably won't appreciably change the ambient temperature in the enclosure.
I'd definitely be using a thermostat rather than a timer for a heat mat used for a hatchling. I would be giving a hatchling snake 24 hour heat and not using a timer. I strongly recommend you to do this. You can probably use the same thermostat later in your big enclosure.
Not sure about timer brands. I definitely remember having issues with noisy timers back in the 90s and early 00s, and then new ones hit the market which were much better; quieter and more reliable, and also cheaper. I suppose these days everything seems to be getting lower in quality (why make something good at a trivial cost when by dropping the price from trivial to ridiculously and pointlessly low you can drop the quality to painfully bad, right?) and I haven't bought a timer recently. It's a shame if we've gone from being able to buy cheap timers to being back to being stuck with garbage on the market.
Not sure what species of snake you're keeping, but most of the snakes people keep don't need high temperature basking spots. That's more of a lizard thing.
Sounds like you're an inquisitive and thoughtful young individual, keep learning and having fun
