Garth and Annabelle,
Based on the above information I believe our way ahead is to use the Waterfall system development methodology.  This approach is really great because its steadily flowing approach..hence why its named “Waterfall”.  I think we need to go through all the phases.. requirement analysis, design, implantation, etc.  Why is this important?  We need to look at our company in a slow and steady fashion.  Since we have to worry about a budget, I don’t feel comfortable taking too many risks.  This model allows us to take a traditional approach, and I believe this will best fit our needs! 
If you take a look at the Rapid Application Development, you will see that this approach is fast development and delivery of a high quality system.  Though it is a high quality system with a low cost, I do not think it’s the best system for this project.  I would like to take the traditional approach, because I think it best suits our needs.
Respectfully,

Your project manager