here is what we did.
took the past 1-2 years average travel requirement and gauged if this would be a true picture going forward the next few years.
planned our travel based on first class (c when no f available). came up with cost (4 pax average including hotel, taxi etc), time taken and compared with various private options.
got all the $/h all in and finally presented to management with our recommendations.
now, if there is endless of funds available you can disregard all of the above and go straight for a BBJ/ACJ.