Getting this person a scope would be no more or less a surprise than taking them to a good astro retailer and letting THEM decide what is best for THEM.
I understand your intentions. But they really only know their preferences. They have the knowledge whereas you are asking very opinionated folks here (

) to make a choice for THEM. There are just too many variables.
My suggestions : gift voucher or surprise visit to a good retailer. It will be a much more personal thing for them this way, & they will appreciate it just as much,