Taxi is a good option. Paris taxis are very cheap compared to here. Paris itself is very quiet in August. All the locals seem to decamp to the seaside.You may find cheap deals in the hotels, particularly those used by businessmen.
Eurostar is very convenient; check in of half an hour for everything, security included, and straight to Disneyland from St Pancras etc; but it can be expensive. Depends where you'd fly from, of course, but if you are fairly close to London then timewise it beats faffing about for hours in airports. Just add up the time that all takes and the stress and there's no comparison.