Hubs are normal 4" PCD jobbies with 1" taper bearings. Should be about £15 each, with bearings etc.
Give the wheels a good clout with a hammer as they tend to rust around the ledge, about an inch in from the lip/bead. If they're solid then give them a clean and a wire brush and a lick of paint and you should be good to go. If they're gone, and need to be replaced, then they're around £35 to £40 for a complete wheel and tyre assembly, from most trailer places.
All the info you'll need to give is the PCD (4" on 4 x 3/8" studs) and the tyre size (which looks like 5.00 / 5.20 x 10), but will be on the side of the tyre.
All the best.