Mostly depends on how serious you want to be about it. I started with one off Amazon for about 30 dollars and soon upgraded to the one linked below. If you have the money to splurge and want to be somewhat serious about it, go for it. It's great.
As for actual methods, I just watched YouTube videos. But also the one below comes with a book that I never read. I trace all of my works onto the wood before I burn. Freehanding is difficult if you are trying to make it look professional. Other than that, just practice.
I have the Colwood Detailer and love it. With your budget, you could go with the Super pro two pen solution and pick up a couple of extra tips. I use the 1mm ball tip quite a bit.
This is the one I use. Colwwod woodburnerI've never really used the "heavy duty" side so I think it's more robust than I need, but it was a gift so I gladly use it! There are much less expensive ones by Walnut Hollow](https://www.amazon.com/dp/B07GHJYBNQ/ref=cm_sw_r_apan_glt_i_RX3TCB799A0QZKC51ZVV) that I started with and they work great for the average[ user. If you burn a lot/veey datk/everyday, you may want something more robust than Walmut Hollow though. Hope this helps! Happy burning!