I ended up buying a "mini-PC" as my router. It's quite a bit over your budget, and you'd need an AP of some kind for WiFi. I run proxmox on it, and pipe the NICs through to my OpenWRT VM. The performance is great, and given it has 2.5gbps NICs, it's somewhat future proof. UK Amazon link to the one I bought: https://amzn.eu/d/1pqfQEk

Sounds like you're trying to run a decent little homelab, so I would personally recommend going with prosumer hardware. Lots of N95, N100, and N5105 routers available on AliExpress, you should be able to flash OpenWRT, OPNSense, PFSense, whatever you want. I would advise getting one with an i225 or i226 NIC for best software compatibility (support for Realtek NICs can be sketchy).

I waited for a sale and got this one (N5105 version) for $95: https://www.aliexpress.us/item/3256804915099903.html

I got the barebones version, then supplied my own Crucial RAM and a cheap hard drive for under $50. It runs PFSense without even breaking a sweat, and supports 2.5Gbps. There are cheaper options too, but I decided to stick with Topton as it's a brand that's well-reviewed by Youtubers that I watch.

After that, all you need is a Wifi access point. You probably can use your old router in AP mode for now, and then consider upgrading to a newer one later. I bought a Unifi U6 Pro AP and now my home network is incredibly overprovisioned for my puny little homelab, all for about $300. Lots of room to grow if I want to.

You might be interested in the Banana Pi BPI-R4, which has an officially supported OpenWRT image and costs ~US$110.

An alternative could be something like a thinkcentre tiny m700 with a sixth gen i5. It can be found at that price and it's possible to replace the wifi card with a 2.5 gig Ethernet. Then use opnsense or openwrt x86. Mine with opnsense uses 6 watts of power.

But it was such an hassle to properly configure it that if I had to do it again in the future I would just buy the basic Unifi dream machine (costs the same) and have everything done automatically by the easy gui

Acronyms, initialisms, abbreviations, contractions, and other phrases which expand to something larger, that I've seen in this thread:

6 acronyms in this thread; the most compressed thread commented on today has 10 acronyms.

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I'm no expert. Have you looked at the processors that are used and the RAM listed in the OpenWRT table? That will tell you the real details if you look it up. Then you can git clone OpenWRT, and use the gource utility to see what kind of recent dev activity has been happening in the source code.

I know, it's a bunch of footwork. But really, you're not buying brands and models. You're buying one of a couple dozen processors that have had various peripherals added. The radios are just integrated PCI bus cards. A lot of options sold still come with 15+ year old processors.

The last time I looked (a few months ago) the Asus stuff seemed interesting for a router. However, for the price, maybe go this route: https://piped.video/watch?v=uAxe2pAUY50

Look at Gl.iNet routers

Check out MikroTik

Checkout the Banana Pi BPI-R4 (WIFI not available yet) or the older BPI-R3.

Probably not what you're looking for, but I'm going to note that Turris make some great OpenWRT routers.
Currently running theTurris Omnia, and using both Wireguard and Yggdrasil through it.

Assuming your old router might survive as an access point, maybe consider a Protectli FW2B? https://protectli.com/product-comparison/

The good news is there a tons of devices that can run openwrt. It depends on what you want to accomplish

Way over your budget but if you can swing it the UniFi Dreammachine is amazing. I can’t recommend it enough and was super easy to configure for my fiber internet at the house