could you fly from Luton with Easyjet to Paris CDG airport? Thats what I do, then get a shuttle transfer from CDG to
Disneyland Paris (and back if you prefer).
For hotels it depends what you want, I usually book in low season with a deal for the onsite hotels through Disney themselves (including the Santa Fe). My budget for onsite is £300, and I try to get as many nights and days in the park as possible for that

. I'm considering a next trip in February next year, because Disney is doing a deal where you get 4 nights onsite for the price of 2, and your son is free at that time of year too (so you could have 4 nights and 5 days in the parks for £267 total for the both of you, staying at the Santa Fe or Cheyenne hotels).