Advice Needed: SMS offline Marketing

Ok, for some time I have been using Text Local to keep members of my social group (football team, different meeting groups Etc) up to date with what's happening.

I have now thought why don't I offer this to local take away shops and restaurants within my local area.

I am going to offer a managed SMS marketing service. I will (am hoping) charge an initial set up charge then a monthly recurring fee. This is were I would like some advice.

What can I charge monthly or what's the best way to work it out per business.

My initial set up charge will cover the purchasing of the key word + a little extra. I'm thinking around £150 set up then monthly charge.

Is anyone currently offering this type of service? And if so would you be willing you advise and work with me to help me get this up and running.

Like I said previously, I would like to offer this to local businesses within 10 miles of my location to start before branching out to other locations.

Thanks in advance for any comments and advice.

John.

ps. Sorry if this is in the wrong section. It's also in mobile marketing.