If you want a fantasy gown I would get quotes from someone who sells at Ren Faires. Most of them will take custom work if you give them your sizes and on the whole I've found the Ren Faire community to be plus size friendly. Plus if they visit your local faire they'll usually let you do pickup there, save on shipping! You might find someone selling similar crowns to the one you like too. Winter is the best time to contact sellers about custom work because it's the off season for most of them.
Most Faires also have wedding venues. You can get some really magical photo ops. Be forewarned that they will also probably be all outside locations and may not allow outside catering. Some will let you have weddings during the faire! Which can be really fun for you and your guests, but you also have to deal with other regular patrons.
I used to work at Scarborough and then for one of the founders so I have too much knowledge of Ren Faires lol. Idk how close you live to Scarby but if you're interested I could probably get you info.
My sisters recommended
The Knot to corral all your information, check vendors, etc. We diyed, borrowed, and thrifted a lot of stuff for her and our other sister's wedding. That's definitely the way to go if you wanna stay in budget. A lot of diys are pretty simple; we even set my dad and brother to task and neither of them are particularly crafty lol. We had the aunts cater my baby sis's wedding potluck style and my middle sis had the sides catered and her new in-laws brought the meats.
I could probably infodump more but I'll leave it at that ^^;