B-Race / Training Wheels

I know, another newbie wheel question. Sorry.
I have Xero XR-1 wheels on my bike, and the the rear wheel has cracked around one of the spokes. I need to replace it and I am having a hard time deciding the best replacement. I didn’t particularly like the XR-1s, and I want a really durable wheel to train on. However, I do not have race wheels so I need to be able to race on them too.

For my A-level taper races, I am going to rent race wheels, but Im not going to bother for lower level races. So my new wheels need to still be able to go relatively fast. Durability is #1 priority, but I would like an aero benefit too.

Should I replace my whole wheelset or just look for a back wheel somewhere? My budget is $200-$600, depending on if I get a wheelset or just a rear. I only paid $800 for my bike ('06 fuji aloha 1.0) so lets not get carried away with Zipps. I’m an Olympic distance athlete 175 lbs. I’m at the top of my age group in most races. Most of my rides are flat but windy (Florida).

Thanks for your help/ advice.
Looked at: Mavic Ksyrium, Ultegra/D-A Mavic Open Pro (Ebay has one for ~100), Bontrager Race Lite

OpenPro with a wheel cover on the back, dude. Cheapest option, and aerodynamically just as good as a disk.