CDG airport to Gare de l'Est by RER

The RER goes to Gare du Nord which is just a few minutes walk from Gare de l'est. I've never used it but I guess you could say it is a "convenient ride". Costs about €10. See parisbytrain.com for further information.

As Norma says it ran about ten euros(9.75 last time I was there but it may have changed a bit) and it is easy I would(and have ) just walked to Gare l'Est,its like ten minutes and I have done it with a child and luggage!
As long as you can handle your luggage and don't look frazzled and overloaded,otherwise you may attract the attention of a pickpocket, they look for that sort of mark and hang around the train stations. Have route to walk already mapped out.