I priced What's up Cupcake (it appears their site is down but here's their Yelp)
http://www.yelp.com/biz/whats-up-cupcake-houston
For 300 mini cupcakes in 3 flavors, delivery, set up and rental stands they wanted like $450. I found that reasonable.
And then priced these folks in Katy:
The Iced Cupcake
http://www.yelp.com/biz/the-iced-cupcake-katy
They quoted me $11 a dozen for anything under 250. When I told her we needed 300 and we wanted a small cake for the "cutting" ceremony too, she said that price per dozen would come down some. She didn't commit to a number but even if it's a dollar a dozen off, that's only $250 for the cakes, then she said it's like $30-$50 for a cutting cake. All free delivery. That leaves $150 for stands and trays, etc. though we didn't discuss if those were included. They may be.
Their site is down too apparently but I know for a fact they're up and running. They're right next to Freebirds on Mason. Good cakes, very reasonable prices. Don't know for sure but the owner I talked to was wearing an Aggie shirt so it may be Ag owned.
Give them a shout.