Taxi fare from Udon airport to Udon Thani

As far as I am aware taxis waiting for hire (& tuk tuks) are NOT allowed at the airport. There is a service that is, basically. a mininbus that does a circuit of Udon dropping off at hotels. Tickets are available just before you exit the airport - I understand that the ticket price is pretty minimal.
As Tex says many of the larger hotels have a mini bus service & it is possible to avail yourself of those for a few baht to the driver. Charoensri Grand is probably the nearest to Top Mansion that does.
Top Mansion do not have their own mini bus service. However I am sure if you contacted them then they would arrange a pick up for you - Tex is pretty correct about the likely charge!!

Wayne I am sure that if you phoned the Udon meter taxi service from BKK airport & told them which flight you were on & where you wanted to go that they would meet you.
The 'no taxi/tuk tuk' rule is to prevent touts hassling unsuspecting visitors & not to prevent passengers making onward travel arrangements. The metered cab service is by appointment only & they cannot be 'hailed in the street', so I think it is highly unlikely that the authorities would worry the driver of one of the cabs parked in the car park waiting for his fare.

Its no problem for the taxidrivers to park at the airport parking. I only call them and they stay waiting for me at the arrival......by the way.........this is the sheapest way to go alone and you dont get rip up by some tuk tuk or limoservice!

My mate was here recently and chose to stay at the Centara.
He was asked 400 baht for a ride to the airport on the Hotel's minibus. So we're not talking big money here, but still a rip-off in my book - not in comparison perhaps to UK costs, but I know you can travel in a taxi across Bangkok for less than 300 baht, including the tip! And the minibus goes to meet the incoming flight anyway.