I started with a Rockchucker that I still have and use regularly.
When my ammo appetite grew, I got a Dillon 550. The 550 is capable of building top quality ammo, but I usually won't fire it up unless I'm going to load a big batch (3-400 rds or more).
For bench rest quality rifle ammo, I would prefer to weigh each powder charge and for this you can't beat a single stage or turret press. I guess there is no reason you couldn't use a single station on a 550 as a single stage press.
Leftoverdj has a good idea. Buy a 550 for your high volume stuff and shop around for a used single stage. They can often be had inexpensively at gun shows, E-bay, or asking around at gun stores.