Hi Joy! The Tinkerbell Half Marathon is a really fun race! Be prepared to see a lot of pixie-dust and wings along the way! The medals are precious, too!
You are wise to stay at a Disney resort. I was amazed during my first Disneyland trip at how convenient and close everything is together. Your resort, both parks, and Downtown Disney are right within a short walking distance from anything!
Obviously, you want to do the Disney "classics" at
Disneyland Park. These include things like Space Mountain, It's a Small World, Dumbo the Flying Elephant, Jungle Cruise, Haunted Mansion and the Matterhorn Bobsleds. There are a lot of other great attractions too, so be sure and browse around the parks website.
At
Disney's California Adventure, they are just opening a brand new Cars Land with many fun new rides based on the awesome
Cars movies. I highly recommend the
World of Color show, and be sure to ride
Soarin' Over California!
As for prices, it will vary a lot by where you choose to stay. When you register for the Tinkerbell, you will be given access to runner's discounts on resorts and theme park tickets, so be sure to take advantage of those!
I hope this helps. Please let me know if you have any other questions as you get ready for Tinkerbell!