For "upscale" perennials, I go to Tellys in Troy or Bordines (various locations). Your dollar won't go too far, but there is bound to be perennials you've never seen before or you didn't know existed and now have to have. A more reasonable alternative with a pretty good selection is Schwatz's on Sibley in Romulus.
I believe Garden Crossings is the retail arm of Walters Gardens, which is a bareroot and plug wholesaler from Zeeland. They always seem to have the latest and greatest selection. Would be a fun trip. How much cheaper are they then their website, which is pretty pricey.
If you go to their website and click on the Garden Center tab it takes you to the local screen. Midway down the right side is a "Garden Center Login". You can create an account and that will give to the pricing for shopping there.
You can also order everything you want and they will hold it for you to pick up. I find that very convenient especially since its quite a drive for me. Don't want to be disappointed when I get there and all the latest and greatest is sold out!
I get my new hostas from Hallson Gardens in Cement City. They also carry various other lilies, ferns, and perennials. Mail order is the same price as picking the plant in person, but they also include a bonus plant in mail orders.
I also second Telly's in Troy for finding something new. It's nice to just wander around and see the plants in person.
So far, I've been to the following spots:
Blocks, but of course
Van Ottighams (wrong spelling) in Bay City.
Errer's in Bad Axe. Bought lots there. They had a lovely selection of Proven Winner shrubs.
Still will make the pilgrimage to Tellys. I find things there I didn't know existed. That takes a little, since I spend lots of time window shopping on the web.
And, of course, my biggest shopping trip of all, the annual plant sale of the Belle Isle Botanical Society next weekend at the Greenhouses on Belle Isle in Detroit. And the money I spend there goes for a good cause.