Neither a lighter crank or lighter wheels will make an appreciable difference in your performance.

If you're short on money and have one set of wheels for two bikes, get another set of wheels.

You can build a set using hubs rims and spokes from BikeHubStore. Depending on the parts it'll cost less than $300. But you'll need tools to do it. So if money is an issue, look for sales on built wheels. You can often find decent road wheels for well under $300.