。
Could I maybe buy a different one?
Literal
Different-one [object-を] buy-let receive-could [wondering-かなあ].
買わせてもらえるかなあ layers multiple patterns: causative (買わせる), benefactive (もらえる — potential of もらう), and the wondering particle かなあ. The whole thing means 'I wonder if I could be allowed to buy a different one' — very indirect, characteristic of Japanese hedged requests.