Need help writing a business proposal

I was looking through the classifieds for my city, and was all set to apply for a job. But then I started writing the cover letter as more of a business proposal. Trying to get them to hire my company for their IT work, but I can't seem to get the words into an email properly.

So I'm looking for some help as to different reasons they would benefit from hiring my company as opposed to a full time IT person. The only real reason I could think of was:
1) Hiring us for on-call work would save them money, as they would only need to pay for the contract, which would equate to less than paying someone for 40 hours/day, 5 days/week.

If anyone could help me get something together (even just ideas), I'd be greatful.

Thanks.