SMS mass text and configuration

First of all, I am open to suggestions on how to do this. I am not set on any one application. We are currently using a textfree number at my work to text people who would like to get notifications from our website and local nightclubs. Please see 1stavenuemedia.com. People go there to get there pictures. We shoot at nightclubs. People must text us to get the password for there photos. We want to build a program that will autorespond (same thing everytime) and also be able to create groups and mass text them back. Id like to be able to do this on my phone, but if there is an easy way to do it on the computer it would be great. i dont want to spend more then 25 a month on service. and will pay set up fees for programming or anything else needed. im open to ideas. we currently have too many people texting in too keep doing this manually and texting a bunch of people one by one.