This may be a bit late for the OP's question, but may perhaps help someone else with a similar situation.
If you're spending good money to take a trip, particularly some place where flies & gear may be hard to come by. Take the very best you can afford. If you don't tie your own, or your tying experience is limited, you'll want to have good flies that won't fall apart the first couple of casts.
I'll agree that generally salt type flies are not difficult to tie, but some styles & patterns need to be tied correctly to get the full potential. Just as an example, a Tarpon or Billfish fly that fouls constantly is worthless as you may only get limited opportunities to cast to a fish.
After you've spent a small fortune taking a fishing trip, you don't to blow it because you skimped on the flies. There are far too many other things that can go wrong to ruin a fishing a trip.
I have no affiliation with the following sites other than having visited them many times.
Henry Cowen is a well known fly tier & guide. He has some superb patterns that can fit a wide variety of destinations & species. Henry is also a wonderful person who willingly shares his knowledge. Henry is one of Umpqua's contract fly tiers/designers.
has an extensive list of flies to cover any aspect of saltwater fishing. Very good quality flies, but the prices will not be cheap. Their prices are pretty much inline with many fly shops or the better custom tiers.
It's also a excellent site if you want to tie your own, as most of their flies are pictured & they have some pattern recipes for many.
Lessons in Virginia - saltwater fly tying and fly casting
Capt. Chris Newsome guides in the area of the lower Chesapeake Bay. I'm not sure if he sells flies, but he has some awesome patterns. Most are very unique & again will work for many species.
The link to his site goes to his "lessons" page with gives excellent information on a variety of subjects & includes his fly patterns. Chris is also a great guy who freely shares his knowledge.
Home of Dan Blanton's Fly Fishing Forum and Bulletin Board/Message Board - A valuable international resource for all!
Another excellent source for saltwater information. Dan Blanton is known around the world. Dan is also one of Umpqua's contract tiers.