Rightly or wrongly, the 26" format is not much developed from a performance standpoint. "Lightweight" needs to be defined, I think. My Performer Highracer is a performance bike and built for speed and it has 26" disc wheels. It came with 1.4" tires but I would think nothing of using tires as small as 1" and up to 2" and I would not even get calipers out to measure the width of the rim. Nevertheless I would fully expect to have no issues. I've used all kinds of tires on my rims and have never measured a rim yet. So find yourself a
26" disc wheel within your budget. Call it good. It will be.
Edit: As you can see, decent wheels cost quite a bit of money. You need a 'front wheel' I suspect but we're still talking 3 figures for 'good' (lightweight) stuff. If I wanted a wheel I would hit up a local bike co-op and see what they had available .