Well your price will depend on a few factors.
1) Where in Califonia do you want to fly into?
John Wayne Airport/Orange County (SNA) is by far the closest to
Disneyland. I'd say it was maybe a 15 minute drive in light traffic and that's because we were driving ourselves and didn't know where we were going at first. John Wayne is not a huge airport but is a very easy to navigate one. There are a few shuttle vans or buses that you could take out of here in order to get to Disneyland.
LAX is the largest and often the cheapest (but not always). They will have the widest options as far as number of flights and times available. There are many more ground transportation options here as well. However, you can expect the drive time to take anywhere from 45 minutes to 90 minutes depending on traffic.
You could also fly into Long Beach (LGB) or Burbank. both of those are smaller than LAX but not quite as close as John Wayne.
2) Are you flexible with dates you travel and times of day?
I've had excellent luck using sites like hotwire or priceline to get reduced travel. Often half or 1/3 of what the going rates would have otherwise been but I'm willing to travel mid-week at off times.
As far as prices, I would visit travel websites like expedia, orbitz, or travelocity to get an idea of what flying out of Milwaukee would cost. Sometimes flying out of Chicago is cheaper. I've gotten great rates out of Madison or Green Bay on occaision but you have to be willing to shop around and check often.
Good luck!