I don't know much about UL but I can say that FCC certification (also technically required) for electronics can range from about $3k to something like $30k depending on what you're doing.
($3k would be for "unintentional radiator" device, i.e., not supposed to be a radio, $30k would be for "intentional radiator" device, i.e., supposed to be a radio)
FCC ensures a product doesn't cause radio interference, while UL ensures the product is safe to use and won't cause fires or electric shocks. For DIY, your primary concern is UL certification.
Because of customs product import rules, that FCC stamp is often not optional. Now if it was a dodgy seller, the stamp will not match the physical devices on rare occasion. =3