How much would the Beagle cost if it were launched by itself?
Odds are, its cost would be comperable with the Mars Pathfinder mission. Mars Pathfinder cost somewhere in the neighborhood of $200 million if memory serves. Something like half of that cost was for the booster and mission support costs (personnel for navigation and TT&C, DSN range support, etc).
I don't think the Beagle had to pay much if anything for launch and mission support on the way to Mars because it's a secondary payload. You're talking about an apples and oranges comparison to directly compare it to Mars Pathfinder.