Same thing happened to me a few years ago. Especially if you only pay for a lower speed of service, a newer modem won't make much of a difference. I replaced my DSL modem with the wifi one only because that was the only one Best Buy had in stock at the time. I disabled wifi and the routing capabilities of the modem and still used my router with the new one.

I think they're pretty much commodity products. Just buy the cheapest one.