Well, that’s a bit hard to nail down, the board is not for sale yet so, I’m not sure the price is nailed down. The plate is laser cut acrylic I got on special from elecrow for $4. The Keboardio keycaps were on sale for $5 a set for the alps version. I went cheap and got Matias clicky switches (alps clones), $40 for 200. I also used half a roll of filament for the case, about $20, and screws I had on hand. All in, disregarding prototype cases, around $280 to $300.

Your best bet would be to look at the datasheets for the OLED or RBGs you want to use. I think most RGBs that are addressable that are commonly used are 5v