Like any hobby, you can spend as much or as little as you want to get started. Much also depends on where you plan to hunt - if beaches, streams, or lakes are involved, you will need a waterproof coil at a minimum, if not a waterproof control unit as well.
I typically hunt old farmsteads and the occasional city park. I also will sometimes hunt shallow rivers or creeks adjacent to old farms/home sites.
Prior to the pandemic, I went every year for spring break to South Carolina to hunt with friend that's been a relic hunter since the early '70s and hit some civil war and revolutionary war encampments on private property where he has permissions.
The best piece of advice I ever got was to buy the best detector you can afford - there are lots of cheap detectors wrapped around trees for a reason.
I also recommend buying from a local dealer, if you can find one, rather than a big box like Kellyco. I have nothing against Kellyco, but your local dealer will typically fix or repair issues onsite. Think of it like buying from PSA, BCM, Primary Arms, etc. vs. your local gun shop.
My personal recommendations are one of the following - all are good and proven detectors. Prices go up as the features go up:
Garrett AT MaxGarrett AT ProNokta LegendMinelab Vanquish 540Minelab Equinox 800XP Deus III personally swing a Minelab Equinox 800 for the beach and rivers. I have an XP Deus II that is my primary field/cellar hole/relic machine.
Pinpointers are a must for many. You can live without one, but for $150 bucks it's worth it to me. I have both a Fisher F-Pulse and Garret Carrot. I prefer the F pulse over the carrot.
The other best piece of advice is to spend a whole lot of time learning your machine. Each one responds differently and the sounds and visuals vary from machine to machine. Read all you can, buy any "how to" books that might be out there related to your machine, and watch youtube videos. There are ton of them out there.
I prefer to carry when I hunt bigger city parks. However, appendix carry while detecting sucks. 4 o'clock or 6 o'clock is your friend in that regard. Ask me how I know...
Good luck, let us know where you end up and I am happy to share whatever info I have. I am not an expert by any means, just someone who has dug a lot of dirt and junk over the years.