Kristyn: First off, I bought orange and white tiger lilies at the end of spring last year for a super low price at Joann's. I think for my centerpieces and bouquet flowers together cost me less than $30!!! So I definitely suggest looking out for sales. I just bought the extra white lilies I needed for my bouquet at Michaels on sale and they were $.89 for a bunch of 6 flowers! Can't beat it!
As far as putting them together goes, I just cut the bunches apart, put together the flowers until the arrangement looked nice, and wrapped it with floral tape (AC Moore or any craft store). Then I wrapped white ribbon down the stem and back up (secured at the top before and after the wrap with a plain silver sewing pin). Then I took orange ribbon and cris-crossed it down the stems, tying it in the back on the bottom when I was done. My mom put a little clear elmers glue across the criss-crosses in the back of the bouquet to make sure nothing shifted, and you can't even tell its there.
Honestly, there were pretty easy and extremely inexpensive to do myself. Just for the bouquets, I can probably estimate that I paid about $20 to get 5 girls bouquets and my bouquet done -- and I had them all done in a matter of a few hours!
Here is an upclose pic of my bouquet (we put white pearl flower accents in mine and made it bigger to stand out from the girls' flowers):
and just in case you're interested ) -- and also because I feel very accomplished for all we got done yesterday -- we also made the guys' boutonnieres yesterday too! We just bought a basic boutonniere flower stem at AC Moore for maybe $1 or so, and hot glued white and blue ribbon, the starfish and a bin back on them.
The guys are wearing orange shirts, so they should stand out nicely: