Silver and white are generally considered the same kind of rum...clear/light white rum = clear rum = silver rum = light rum = Puerto Rican rum they are basically the same (this has caused confusion for me when buying in the past.) Brazilian Cachaça is similar to these, but is stronger and a conversation piece for a party.

If the drink he is making involves citrus, he can go even cheaper (Castille is good.)

Bacardi (Bacardi Carta Blanca if you want to get $3 fancier) is standard, but watch out for the higher proofs, sometimes you'll accidentally get a 150 proof when you were reaching for the regular stuff.