Bob makes some excellent points.
Also I would add that ROI is very difficult to quantify. There are a few professional firms that track and detail exposure from all sources of media and on-site (and are very expensive to employ). There really is no concrete industry standard when it comes to print, TV and web costs.
TV time (local/cable) depends on channel, demographic and geographical reach.
Same for print, and internet ( i.e. cpc and cpm ) impression costs seem to vary greatly.
So formulating a ROI can be and is very difficult.
I was performing this as an end of the year report to my sponsors, but the varying costs of exposure time in all media's made it nearly impossible to pin down realistic numbers. So, instead I began to compose Cost-Benefit Ratio Reports. Which for my application made it easier to quantify the C/B's of sponsor involvement.
Basically, a sponsor wants to know and see a "Benefit" which can be in the form
of direct or indirect sales. Or even just brand exposure. It is creating a potential
sale or use that is important, but not the be all end all either. Good will can go
a long way.
As far as proposals go, I would also add a 'Media' section - where you detail some of the outlets you could provide exposure. Local cable channel, local/town newspapers, and of course a website. You could run a food drive in your town and invite the local rag to cover it. You could have some team members volunteer at the library to teach kids to read or whatever else they may need in the way of volunteers. Maybe work with the PD to run a bike safety clinic, etc. There are many ways to provide exposure to a potential sponsor - just make sure it is always positive, and if it can relate to their business even better!
When you request cash/money from a potential sponsor, you have to understand the "opportunity costs for the potential sponsor." Meaning, if you request $500, from a potential sponsor, you must realize that the $500 could be utilized in other ways. So, you need to show how you can maximize those dollars, in which you and your team can provide more benefits than say a small newspaper ad, or local cable commercial, and so on would. Bang for the buck so to speak. Always track and record every single detail as well.
A print ad will run in a few editions perhaps, same for the possible cable commercial, but you and your team could and should be promoting a sponsor all year long. That might be the difference in getting the money. Plus, having yourself and team members readily available provides the potential of creating a more personal relationship than say the newspaper or cable sales rep.
Each member becomes a "representative" of said sponsor. This can be a great marketing tool...or a disaster depending on the members themselves. it is extremely important to stress this to each individual of your team. Remember, first and foremost - your team is a Business, not a hobby, a game, or sideline.
Think like this, convey this message and always be professional. It goes a long way.
Good luck and keep us posted on your progress.