With regards to time, cycling for me is more expensive. I've often thought of the rare days of bringing in the car 'oh this is so easy'. Assuming you get in early (like me at around 745), you don't have parking issues and the traffic is quite light.
Car: 20mins each way - total around 40 mins. Let's say 50mins to be generous.
Cycling: 35mins each way. Locking/Unlocking bike: 5mins. 20mins extra shower (at work). Packing bags in morning (extra clothing, etc) 10mins. Getting changed at work to go home - 10mins. Weekly half hour of bike maintenance (5mins per day). Total: 120mins. Over double.
Going back to your comparison ... where do you park...? In a staff car park or do you have to find a space or pay for one?
When in the car, we have a free staff car park. Trouble is, there aren't enough spaces. If you arrive at 745 like me, you can pretty much park anywhere. If you arrive after 9, you can forget it. Work have secured a car park about a mile away with a bus shuttle service, but it's all a bit of a faff and can add an hour to your day easy (by the time you've fought back through the traffic you've just crawled through, then waited for the bus....) - so this leads to a bit of a war to get in early.
When on the bike, we have a bike rack outside of the main building but it feels fairly secure. On a good day it actually fills up, so we've been encouraging work to install a second one.
I did suggest to work about a scheme where if you didn't use the car park you got a tiny payment of 50p per day. This would apply to people who worked from home (which they encourage 2 days a week), people who car-share, walkers, bus users, and yes - cyclists. Would reduce the demand on the car park for not a lot of money. Largely fell on deaf ears though.