I've had pretty good experiences with https://42keebs.eu/ and https://keeb.supply/ for my two split keyboards. They both offer kits and assembly services. I especially like that acrylic covers from 42 keebs, and they hand write a greeting on the receipt, which always makes me feel quite nice, haha.
For a first build I feel like QMK firmware with Vial support really made it easy for me to configure the keys how I like. My second keyboard used ZMK, directly modifying config file is not exactly hard, just a little more daunting.
I did ask a colleague to teach me how to solder for my first keyboard, he spent 10 minutes explaining, I practiced a little, and then I soldered everything without too much issue. I enjoyed it a lot, but it's probably not for everyone.
I also quite like https://splitkb.com/ with their super easy customizable designs, but never really went for that kind of budget. They should be within your budget though, you should check them out.
