mine was covered by my insurance entirely (my states Medicaid) but generally 40$ is the cheapest you can find it without insurance or services like GoodRX. It's all testosterone cypionate, I think ive had a few different brands and generics over the years as my insurance covers different things occasionally but none of them effect me any differently, but I inject mine subcutaneously in the fat on my stomach mostly because I have a fear of both injecting into a vein and aspirating to prevent it and that avoids both. Needles, syringes, alchohol pads, and even the sharps box are all usually fairly cheap typically a months worth of that stuff runs me under 20$ even including the box that lasts a lot longer than a month.
There are a ton more effects, usually within the first three months you'll see voice changes, an increased sweating with some scent change, skin oiliness, energy, hunger, libido, likelihood for vaginal dryness, the beginning of bottom growth, and your existing body hair may begin growing in a bit darker. On top of that because of the libido change you may have some changes in the way your sexuality presents/how you view your sexuality and you may also lose the ability to cry, or at least produce tears, as much as you can currently. You have a high potential to stop menstruating starting during this period but some do not stop or still have spotting even a couple of years into testosterone, this may also increase your risk for ovarian cysts. I cannot stress enough how hungry you'll get, in my household we call it testosterone hunger and it usually causes us eat like twice our body weight in protein so really make sure you're stocked up on your favourite high protein foods during this stage. Other than that my only advice for this stage is to adjust your shower schedule to accommodate how much more sweat and oil you produce especially if you start during or right before the summer, I personally intentionally started in fall for this reason.
Around 3-6 months you'll see body fat redistribution, muscle mass and strength increases especially if you exercise as much as you can, bone density increases, maybe some height growth at your age if your plates havent fused yet, body hair growth, and I personally noticed an increase in earwax production around this period.
6-12+ months you should see facial hair growth, potential male pattern balding, and eventual Adam's apple growth but that frequently takes a few years. Because AMAB and AFAB people frequently have different likelihoods and signs for a variety of conditions like heart attack, stroke, and some genetic conditions, testosterone in AFAB people slightly increases the risk of stroke and iirc I believe pulmonary embolism and it can change the signs/symptoms of things like heart attacks from the female signs to male signs.
Genetics play a lot into how testosterone effects you, this list is largely a guideline based on what is typically seen, some people on testosterone see changes at different times than what is listed or don't see some of these changes. For example I guy I knew started growing facial hair 2 weeks in, another guy I know has been on it as long as I have and hasn't grown a single hair. Similar thing happened to my cisgender brothers too, the older one started patchy facial hair at 12 and the younger one is currently a 26 year old with only peach fuzz. Also keep in mind that this guide is when these changes BEGIN they will keep changing and when they end is up to your body and genetics, even I'm still getting bottom growth, body hair, facial hair, and I've barely started Adam's apple growth so don't freak out if you feel like it's not happening fast enough.
(For anyone else if I've missed anything feel free to add it)