So I was giving this challenge some thought. Your goal is "name" casinos in near mint condition. I propose the following:
A Vegas casino mixed set similar to what
@David O showed above. This will allow you to have multiple name casinos in one set without repeats. Don't have two denoms from the same casino because then it feels like a set from that casino with a few chips from somewhere else.
This allows you to acquire Vegas fracs from known (Binion's Horseshoe) or lesser known (Joker's Wild, Railroad Pass, or Main Street Station) casinos in very good condition. You can then get mint/near mint live dollars from places like New York New York, Paris, Venetian (or a host of others). You can get mint/near mint live fives from the same list of casinos (just don't repeat). Perhaps a member in Vegas can harvest these for you for a small fee. For your $25 and $100 you can look into the more collectible chips (since you are buying fewer) from closed casinos. This would include the Dunes that you have excluded, but also Tropicana. If you opened the location up to other venues, you could include Horseshoe Cleveland/Cincy... there are a host of other casinos but I don't believe they are known enough for your criteria (Empress, Casablanca, Grand Victoria...)