it would depend on the size of the group there are private transfers but if it is only for a few people works out expensive
you can get a bus outside beauvais airport that takes you to porte maillot in paris 13euro per person and then the train sation is accross the road to get to disneyland its fairly cheap but the whole journey maybe takes 2 to 2.5 hrs it is fairly easy i have done it a few times before if you search beauvais transfers on search engine it gives a few sites that give quotes for transfers and you will probably find the site for buses also
There is a list of Private Shuttle Companies on the Very Useful Information sticky here, just scroll done the page until you come to it.
Also see this thread here, although there are a few other private shuttle companies to chose from other than this one, this is the only one l've used as l've been happy with the service.
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