You can re-program the keyboard using free software firmware such as the QMK Firmware. Also - you don’t need any special tools to program the keyboard. Resetting the keyboard puts it into a special mode where you can use standard tools such as dfu-programmer to flash the firmware to the keyboard’s micro-controller.
It is possible to extend and modify the hardware, repair it and even assemble it on your own.
Most keyboards that are promoted as programmable are only programmable using a special, keyboard specific programming tool. Or via a special in-keyboard method of changing the layout or programming it. It does allow you quite some freedom to customise the keyboard’s layout and functionality. But it does not allow full freedom to re-program the keyboard - much less using free software.
Quite a few of the keyboards supported by the QMK firmware are bluetooth capable (and hence, wireless). You will find other bluetooth builds by community members as well.
The parts are individually very costly and hence, the final price ends up being so high. PCBs are the lowest cost and next are the micro-controllers. However, keycaps, switches, cases and plates are what add to the cost of a mechanical keyboard.
Mechanical keyboards of this sort are not mass-market items. They are produced in small quantities and for a small group of keyboard enthusiasts. That increases prices. And another thing that increases prices is the quality and inherent cost of manufacturing various components.
But don’t let that discourage you! We are all here to help and support you in your journey to hackable mechanical keyboards.