That router is so old almost any router you find will be that fast. I would not go really cheap though. I would get at a minimum a router that claims 1200 speed. Many from the larger name brands can be had for the $50 range.
Routers with larger numbers are not necessarily better or faster. 1/2 the connection is your end devices. Your end device for example would have to have 4 antenna to support 600mbps on the 2.4g channel. Most end devices only have 2 so they are limited to 300. Not that you will get anywhere close to either of those numbers.
You need to consider your end devices ability when you select a router. Only you know if the extra expense is justified.
Although it may not matter your current router...