Suggestions for a small router that only needs to be a gateway?

We have a legacy router we would like to repurpose that only serves as a gateway for a few devices. The devices that are connected will all be eventually setup on our main router, but those devices are not easy to configure and it will take time and various maintenance windows to finish. We want to reuse this older router as soon as possible, considering it has a lot of good features. In the mean-time, as we transition those old devices, we want a small router that serves as the gateway for those devices.

Any suggestions? It will literally do nothing except serve as a gateway. I've been told that max we can spend on it is $300, but I honestly think that's too much.