Check our Marie Gabrielle. I do not know what kind of minimums they have, but it is a restaurant with a gorgeous garden they open up for ceremonies. I can't describe it - you just have to see it for yourself! I have had lunch there a few times, and my meals are always excellent.
You might also take a look at Avanti Fountain Place:
I had mine at the Seventeen Seventeen Restaurant at the Dallas Museum of Art. The restaurant has a outdoor patio where we had our ceremony, then reception dinner inside the restaurant. It holds about 100 guests if you choose seated dinner, more if you do buffet dinner. The price is gonna be a bit more than your budget, I think. We had a great time, the food was great and I thought it was worth every penny. The Seventeen Seventeen is operated by Wynnwood.
Guess I should have asked how many guests also....
Anyway, have you looked at the Arboretum yet?
Or the Nasher?
Just about any restaurant will let you do a "buy-out" if you give them enough notice. But doing everything on-site at the Nasher would be very, very nice.