Recently, there's a newly open shop in JB renting/selling wedding gowns called "Sere Vella Gowns Gallery".
I have visited them once. Their wedding gown varieties are not many (because newly opened).
Rental from RM600 and above (for 3 days). Selling price starting from RM 1,000 and above.
They do have many variety of evening gowns from RM 500 and above.
You may go over to have a look =)
I personally think, KL have more choices for custom-made wedding gowns/ready made gowns with better price.