The wifi chipset, CPU and Memory are the parts that count, maybe also the ethernet ports and usb. So if you wanna buy a good but cheap router, I would buy a used one that has reasonable price and good specs.
I'd also prefer support for Wifi 6(e), but if you are on a budget, old standards high end hardware is really cheap on the used marked.
So here is what I recommend: Look at the OpenWRT list of hardware filtered by ax[1], sort by CPU MHz and look through the table for a good Mediatek / MT chipset in the column WLAN Hardware (the CPU sorting is "alphabetical", not natural, so it might be that the most powerful ones are in the middle of the table).
I recommend:
- Ubiquity Unify (AP - if you need a router, don't buy)
- AVM Fritz!Box 7520 / 7530 (not in the list, but a german bargain)
- Linksys E8450 (aka. Belkin RT3200)
- GL.iNet GL-MT6000
- Asus TUF-AX4200 / TUF-AX6000
- BananaPi BPi R3
- Xiaomi AX6000 / AX9000
- Netgear WAX220 (AP)
Might make sense to get a different brand or model that is more economical.
Simply storing something for decades has costs, which factor into the price.
As for the general upward trends in capacity and price, of WiFi gear, we're now at the point where they are using multipath and phased array antennas to get around the Shannon limit on Data transmission, effectively using the same channel more than once. It's fscking magic!