Sponsor $ contribution depends on a lot of things. I can tell you that the marathon I work for has less finishers than yours, but also has a related event so our total participants is about double yours. Our title sponsor is in for somewhere in the range of $60k-$90k/year, to be real general, and it's a 5 year commitment. For this they get exclusive event naming rights and we are not allowed to have any sponsors on any level from any business that could be considered a competitor of theirs. We are allowed to "sell" other parts of the event to other companies, such as the water stations are sponsored by a local supermarket and the race expo has its own title sponsor. We're also allowed to have 2nd tier/3rd tier/etc sponsors such as a beer company sponsors the post-race party and a water company is a sponsor for product and cash. Those below title sponsor entities get t-shirt placement or confirmation magazine/results magazine coverage-depends on the specific arrangement.
When figuring out how much this is worth to your company look at the total coverage you can get. If the race is good at linking your name to theirs all the tv and newspaper coverage will splash your name. It's often hard to justify sponsorship from a pure dollars and cents standpoint but if you look at what this can generate from additional angles (and the race is a good community event) it can be a home run.