I have to wear boys shoes all the time. I'm a UK 5 most of the time (US 6?) and that's the upper limit for boys shoes, and extremely irritating. A lot of places don't seem to stock them as much as the sizes that are definitely male or children's.
They are cheaper, but there's a reason for that which isn't just theat they're smaller, or that they're not taxed here in the UK (adult clothes are, kids arent), they're lower quality. I have a pair which I hate wearing now because the wind blows through the hole in the side, and the bit beneath the insole had worn away so that the sole feels kinda spiky after wearing it for a long time. On the other hand my assault boots which are unisex so available in smaller sizes are still perfectly wearable after 5 years.