A group of us flew on the inaugural BHX-BVA flight last October, flights were fine, flying time on the return leg being about 50mins.
The flight outbound was somewhat longer as fog and the lack of a decent ILS meant we had to hold for nearly an hour !!
Beauvais Airport is about 70kms from Paris, however, the very quick transit through the very small airport and coaches timed to depart after each flight arrives ensures a quick transit to central Paris, so I guess under 90 mins from landing to city centre.
Which I expect is no longer than flying to CDG etc.
The most expensive part of our day trip was the price of the beer in the bar at BVA (€6.00 a pint)
Ian