I have strong feelings on this one, having spearheaded DIY flowers for a couple of friends’ weddings, now seriously weighing whether or not to DIY my own, and working on a BIG “7 deadly sins of DIY flower arranging” post for http://www.floretcadet.com to be a reference for people considering it.
First, I’m all for it IF there’s a real desire to do it and you know what you’re getting into. If you don’t care about flowers that much and just decide to DIY strictly to save $ you will probably tear your hair out and you’d be better off coming up with non floral decor. It’s important to understand that it’s a lot of work, takes real calculation and planning, takes up a ton of space (as in can take over a house completely for a few days) is messy, and usually requires a team of dedicated helpers to pull off
I think Fifty Flowers is the easiest source for wholesale flowers online, but there are wholesalers who ship direct to the public who have a bit of a wider selection (http://www.flowerwholesale.com/ is one), wholesale flower markets if you’re in a big city, or you can order direct from certain farms (https://californiaorganicflowers.com/default) is one, here’s another http://www.weddinghydrangea.com/
You can get wholesale vases here http://www.modernvaseandgift.com/ or Save-On-Crafts and cool retail vases here http://www.jamaligarden.com/
Definitely pay careful attention to instructions about how to condition flowers (they’d come with the flowers you order or you can google, there are lots of sources)
I think your best bet is to choose arrangements that are centered around cool containers (like wrapping or lining glass vases with paper or fruit) or a clear concept (i.e. floral pommander with 50 carnations on top of a trumpet vase) that will be easy to execute rather than something really dependent on the perfect artistic touch or tricky techniques. For purposes of estimating flowers needed and keeping arranging simple, I’d really advise brides to stick to no more than 3 types of flowers, either mixed, or bunched solo in separate containers.
Re: personal flowers, if you are JUST DIY’ing your bouquet and/or bridesmaid bouquets it shouldn’t be too involved – you should be able to do it in a couple of hours start to finish, if you’re trying to do bouts, corsages, flower girl stuff that can get trickier when there’s wiring and finishing involved
I’ll post it here when i finally write my big manifesto on the do’s and dont’s of DIY wedding flowers!