It depends on what necessary materials/resources the team is bringing to the table and what materials/resources the Johnson is providing.
If the run needs the rigger to cover the escape against heavy opposition then the rigger is going to need more cred. If he is going to have to risk major damage to over 200K of drones that can't be traced back to the Johnson's corp, then the Johnson is going to have to lay out more cred to cover possible damages, spent ammo, and wear and tear plus cred just to get them to be available.
He is renting the use of the drones. More importantly he is renting the use of highly illegal drones about to commit major felonies that can't be traced back to him or his corp. Sure the Johnson's corp has armies of drones, but he wouldn't be hiring shadowrunners if he could just use them instead.
Same for specialized B&E gear, materials to bind spirits, reagents, heavy weapons, special ammo, or even the cyberware of a top-notch street samurai. The harder to get the materials the higher the price.
Now these are materials/resources that are completely necessary to the success of the run. If a mage wants to use the services of three bound elementals during a run and didn't need to, then he is on his own. But if the run requires anti-aircraft missiles, then the Johnson will need to either pay for them or provide them.
Also you also have to look at the risk vs reward of the run. If a prototype is worth millions then the Johnson would be a fool to send the runners in without the resources to pull off the run. So he either ponies up to hire runner that have the resources to pull the run off or supplies them with the gear they need to do the run, fixers being a great way to get a hold of illegal items that can't be traced back to the Johnson's corp. And leftover gear can be made part of the payment.