I don’t know prices there, but VPN at over ~10 mbps really pushes the capabilities of single-core, MIPS-based routers. Some of the multi-core, ARM-based routers start at below US$100 and would be what I’d look at myself. The ipq40xx, ipq80xx, and mvebu units would be on my short list.
Amazon US sometime offers “refurbished” units like the WRT32X at US$100. There may be similar offers for you. (That is just an example. I do not one have personal experience with it.)
Edit: If you’re only VPN-ing in to your own router, Wireguard is an option that many people find robust and secure enough for their needs with much lower CPU requirements than OpenVPN. You should be able to get your 25 mbps line rate on a MIPS-based router if your budget doesn’t permit an ARM-based unit.
Edit: Here's a list (and the posts following) of "interesting" units from a member whose opinion I value. (Ignore the title, as the thread was about more than that initial question):
Top ten routers currently in use? - #4 by slh*
I'm going to leave your Wireguard questions to someone who uses it regularly.