I'd also see if you can find a Millers Falls #46, 47, 56, 57, or 57B. I've worked with several Stanley and Millers Falls block planes and have always been impressed with the Millers Falls quality and fit/finish. I think their planes were crafted better than their Stanley counterparts. Prices are pretty similar, even though Stanleys are more common. The Stanley 60-1/2 is a great little plane and will serve you well, but the Millers Falls might be worth your look.
Sargent also made decent planes under their own name and for others (such as Craftsman). Older Records are also good quality tools. Keen Kutter, Footprint, Ohio Tools, and a host of others made block planes, some junk, some quite nice.
Whatever you buy, i'd recommend a few things - adjustable throat and screw type depth adjuster (less slop than the adjustment wheel configuration). I've had problems with the knuckle lever cap assemblies holding the cutting iron firmly, and i really do like a lateral ajustment - not necessary, or even prevelant, but certainly useful.
I'd stay away from new planes in that price range. You'll likely get frustrated to the point of not using the tool anymore if you purchase a junk tool. Anant and Stanley both make very serviceable block planes, but both will require some tuning to get them to work well (i've got a 10 year old Stanley standard angle block with an adjustable throat - it's a really good plane that gets a lot of regular use. I think they're about $50 these days). The Groz planes that i've seen look somewhat crude, and the Buck Brothers planes i've seen at the local big box are a waste of money in my book.
Paul Hubbman