So I felt this way myself, but after having just put together a DIY EC TKL board, I’d suggest reconsidering, especially with your price range.
A full set of Deskeys parts for a custom TKL build is $282, and that’s just for the domes, housings, sliders and stabs. You’ll still need a plate (mine was around $70; unless it’s a kit, you need a custom one), a PCB from CK (currently out of stock, but another $65 + $8 for the daughter board). So you’re at $425 and you don’t even have a case yet. And I didn’t include shipping, taxes, or tariff nonsense. There are cheaper parts options, but I wouldn’t recommend them due to fitment issues.
Meanwhile, a full price RF TKL is just under $300 at MK dot com.
If you want something more custom, kits are definitely the way I’d go if I had to do it again, but are still pricey. E.g, if an 1800 layout is your jam, the CK980 GB running right now might work. It’s a bit outside your price range – $385 base EC option plus $155 for the Dynacap kit runs $540 before taxes/shipping.