You can buy an off the shelf router such as a higher end Asus router which has a VPN server built into it. Then just follow the setup steps for the VPN on the router.
The problem is, VPN requires alot of processing power, many routers can't handle much VPN speed, like 30mbps for most routers. For high end ARM routers, they can hit about 100mbps of VPN traffic. For anything more, it's probably best to build yourself an x86 router and install OpenWRT or DDWRT software on it.
You're limited by your UPLOAD speed on your internet plan. If you have Fiber to the house, you should be fine as they have symmetric download and upload.