Like TheProfosist said if you want it to be unique then it's not going to be cheap. Personally I have spent over a grand on a keyboard myself but that's because I am willing to pay that and have the board 100% to my liking. Some things that you want want to figure out before you dive into the world of keyboards are the switches you like, the layout, the angle of the board, etc. Sadly the mass produced keyboards from Corsair and other names brands won't really be able to help you out in that aspect. A lot of the boards that TheProfosist listed are fantastic boards but at this point will be insanely hard to get, for instance there was only ever 20 made of the TGR-Jane.
I personally like variety so I usually like to try new switches when I get a new board, however I definitely prefer tactility over linear. My main three boards that I keep in rotation contain Vintage MX Blues w/62g 24kt Gold Springs, 65g Tactile Zealios(Gateron made project ran by Zeal), and Vintage MX Browns. All three have varying levels of tactility but similar weights. Another thing to take into account is the plate material. When it comes to customs you'll usually have the option of acrylic, aluminum, and steel. Acrylic is obviously the most bendable out of the three however a little bend is good for tactile switches, I personally love it paired with my Zealios. Aluminum is usually the most preferred option giving a very nice sound and a slight bit of flex. Steel is usually for linear switches(reds and blacks) where there is basically no flex involved.
When I got into mechanical keyboards I was hesitant to spend $100 on board but now I'm willing to spend 10x as much because I understand and like what is involved in them. Your best bet may honestly be looking into Gon's keyboards like Charger said, however if you ask for it to be assembled it can take 6-8 months to arrive at your door. Depending on how much you want it customized it can range around mid $300s to around low $600s or so for a TKL layout.
To loosely quote Eiiti Wada(creator of the HHKB topre board), When a cowboy goes in the desert and he his horse dies he will still take the saddle with him for when he finds a new horse. Think of the computer as the horse and the keyboard as a saddle, I plan on keeping these boards for years to come and enjoy every second typing on them. There are so many options that I could honestly type all day so I'll just leave you with this "mini booklet" for now.
If you still have any further questions I'll be more than glad to help but honestly how I found out what I like the best was by trying new stuff out, it can be quite costly but it's the best option. I still haven't tried everything out either, I still have a lot of learning to do myself but my budget is what's holding me back haha.
