There are many. And prices vary widely. And most will sell to whomever knocks on their door with the 15k+ that is cost to play...
And in my experience you will find that is the sales guy that determine if your price will be at the "wholesale" level (read: low enough for YOU to make some money).
Look at
www.daktronics.com (note: poor reputation in socal)
Learn from what you find there and do more research. As with most stuff, you will find your pricing gets better the more you know about your product when you are talking to the sales guys.
Stuff to consider:
-Install
-color (full hd, 256k, amber, red, green?)
-warranty
-programming / content
-software
-end user support
-tech support (for you)
-controller access (hard wire? Wifi?)