There are many vintage clothing stores in your area that would probably love to buy the dress for resale, and they aren't necessarily going to be the best place for you to take the dress because they will likely underestimate its value in the hopes of purchasing it, or will require to be paid for their services, in which case you will likely get a top end evaluation which may be unrealistic if you don't have the number of a client you can call who you know will pay whatever they need to in order to get the dress.
Realistically, the dress is from the 80s, and although your Scaasi looks to be very nice, Scaasi is not as desirable from the 80s as his earlier stuff is. Neiman Marcus is, of course, a good label so the dress must have been expensive in its day.
Vintage clothing is a volatile market and with few exceptions, like Pucci dresses where there are enough of them out there on a continual basis where you can get a pretty accurate "going price" for them, evaluations can be tricky. If you want a realistic fair market evaluation, one sure way is to put it up on ebay with a high reserve, and pay the feature listing option. You should get a good audience to see it and bid on it up to a level where the value would be. A lot is dependant on condition, material and size as well.
My gut feeling is the value is somewhere between $125.00 and $200.00, certainly not less, but possibly upwards of $400.00 if you got the right people wanting the dress and bidding against each other. I imagine the dress was originally in the $400 - $600 range to begin with.