If you want HHKB layout then I would just get HHKB as everything else will not be the original. It might come with a price tag but it keeps the resale value and it's easy to buy it used while all those custom hhkb-like keyboards you will probably end up buying new and if you have a change of heart your wallet will suffer. I would just try to find cheapest used HHKB2 in good condition ($160 should be doable, actually less than a custom) and if you like it you can mod it in the future. You can install MX-compatible sliders in the future as well as Hasu controller which adds bluetooth connectivity and allows you to reprogram the board. I would enjoy HHKB2 for sure and I thought of getting it but I'd prefer standard 60% layout as I don't need Fn next to the shift, split backspace and due to my native language being polish I need right ALT to be next to the spacebar. I might get HHKB2 as my 3rd keyboard if I find a good deal in the EU to have it in my collection and maybe using it as a daily driver after adding the controller. I think HHKB2 with my upcoming GMK Laser keycaps would be dope.
Edit: As you can see from my signature Pok3r is a solid choice as well. In my opinion nothing beats it in the price/quality ratio and that's why I'm in love with this keyboard. Widely available, easy to buy used, plenty of options even on ebay, frequently on massdrop, takes holtites (hotswap mod, my Zealio 78g Pok3r has holtites installed), very sturdy case and they usually don't ping like other MX boards (I had 3 Pok3rs already and I was surprised none of them was pinging.), programmable* and it's as standard as it gets - you can replace PCB, case, plate, keycaps, whatever you want and for the most part you don't even have to think whether it will be compatible. If someone looks for 60% keyboard I always recommend Pok3r unless they have very specific expectations. You can get it for as low as $70 and I just scored a new one with MX Blues for $85 (unfortunately shipping and EU taxes ruined the price, but still cheaper than any other option, including used in EU).
Unless you want bluetooth I would avoid Anne Pro. New one will cost you $65-75 while for not much more you can score Pok3r, so I would not go that route. There is a sale of Whitefoxes on ebay for $105 so that's a great price for this solid board but I don't like non standard layouts.
Hot swappable keyboards are not necessarily less sturdy. If a keyboard has a metal mounting plate then it doesn't make any difference since the switches pop into the plate anyway. If you can get hot swappable board that has a metal plate then I fully recommend doing that as you can play with different switchces without the hassle of resoldering. I installed holtites into my older Pok3r and I already went through 3 different sets switches so it's fun and easy.
* except couple of keys like Pn, layer mods etc. Vortex supposed to release a software that would allow to fully program all their keyboards but it hasn't been released yet, only teased months ago.
