The AQPK401 has these case dimensions: 35.5mm diameter, 44mm lug-to-lug, 7.8mm depth, and 18mm lug width. It sits well within the sweet spot for small 6.25-inch wrists like mine. Its case is palladium-plated brass with a WR50M rating. It has a domed Hardlex crystal, and a VJ-21 Japanese quartz movement, and is only $40.
For comparison, the more popular AQPJ403 has slightly bigger dimensions, yet negligible, but uses a titanium case, and has a higher WR100M rating. It's been said to be priced at between $80-100. Can't validate this though, since it's been out of stock for over 6 months now in all online stores I've checked.