THANKS!

I'm getting married in January. When should I have a dress purchased by? 

My BM lives out of state and has had some medical issues come up. We were planning on her flying here in May to go shopping but surgery/healing/infection has prevented that from happening. She is due to have radiation the beginning of August and we are looking at her flying in the weekend of August 23rd to go shopping. Is that really pushing my luck or should I go as soon as I can and just share pictures with her? 

My older sister got married last year and spent well over $20,000 on her event.  It was beautiful and turned out just the way she wanted, however I personally feel that a wedding is just a big party.  The average cost of a wedding in my city is $32,000.  My fiance and I just bought a house and would really like to start having children soon.  That said, it's not currently in our budget to throw around that kind of money for nothing more than a glorified party.  I totally understand and respect the point of a wedding and understand that each bride has different views on what her wedding day should be.  However, we are trying to keep our budget within $1500 with 100 guests.  So far with food and venue already chosen, we are right on track to meet our budget.  I think a wedding should focus more on joining families and less on how much was spent on the dress or cake.  Our wedding will have games (Photo Booth, giant chess, etc.), music and hopefully just a really fun day outdoors with loved ones.

For a while, my fiance and I were actually considering eloping.  However, I really want all of our friends and relatives to be a part of our wedding day.  The idea we came up with was to throw a very casual wedding at the local park.  I found a beautiful pavilion there right next to a big open lake and a brand new, large playground for the kids.  My wedding dress will be more of a white sundress (possibly with shorts underneath so i can play with the kids and be comfortable) and I am telling guests on our wedding website to dress comfortable/casual.  I also let them know that heels aren't recommended since there will be a lot of grass around.  The way I envision my wedding day is a bit more like a family-reunion park day where my fiance and I just happen to get married.  There will be no aisle either.  I am thinking of just having me and my fiance walk over to where the ceremony will be after mingling with guests for a while.

The main thing that has been baffling me is that even when I tell family or friends "comfortable/casual... no heels... like a family reunion at the park", they still want to wear fancy dresses and ask me things like "oh you're JUST wearing a sundress?! that looks too plain".  I'm all for guests wearing whatever they want and whatever makes them happy.  My main concern is that they don't actually understand how casual my event is going to be.  I want to focus the panning on what it's meant to be about and not on the overpriced odds & ends.  My biggest concern is that guests won't actually be comfortable the day of the wedding in their heels and dresses.  I honestly wouldn't even mind if they came in jeans.  I've printed on the invites "comfortable/casual attire" and wrote a whole paragraph on our website with a photo of heels sinking into the grass how they should dress casual if they want to be comfortable and that rain or shine the party will go on.  Even after all of this one of the bridesmaids said she plans to wear her favorite dress that she never gets to wear anywhere.  Is there a better way to get this message across or should I just let them wear what they want and they'll learn the hard way?

A line with crystal and tulle in cream pearl satin size 2. 

Any help is much appreciated!