Depends on the state and locality. Some places like PECO here in PA offer something around 3/4 the cost per kWh for business than residential even with summer peak usage. California is much different and has a huge peak-demand rate. Here in PA, I would think that the EV owners who intend to charge at work should be charged based on # of times they plug in per month times about $.15 per kWh used during the charge. If they have a Volt, the most they could use in a day is about 13 kWh (let's leave out driving off for lunch and re-charging for now). In that situation, that is about $2.00 per day. To do the accounting, install credit-card charging stations and all that seems expensive to setup for the # of stations needed. How many stations will they need? 5? 50?
Since a business can somewhat easily setup 120V wall-plugs on 20A circuits, consider having them offer that with a window sticker and simple accounting of a payroll deduction of 20 units (a unit could be $2.00 or something like that). If a driver does not plug in every day, it can be negotiated. It's like the coffee pool (small money) in that the amount paid per day is so small, it's impossible to determine the value of installing expensive charging stations and accounting methods versus keeping it simple to begin with.
220V charing is faster but will employees move their cars after 3-4 hours of charing or "hog" the station all day? Will they have to have a staff member "police" the spots? Will Volts be offered "only" 120V stations while higher-capacity Teslas and Leafs who "require" charging get 220V+ ?
DonC's post is great and shows what a site looks like "after" EVs start over-using the spots. This is why EREVs are so important. Getting a re-charge at work for a BEV may be harder to do than you think. EREVs adapt - BEVs squabble.
I have a business model idea that someone could run with. BEV recharging "servicemen", basically low-wage employees who arrange for the jockeying of recharging among a parking garage full of EVs. If there are 20 EVs at work, these guys would utilize portable recharge cords within the EV "bay" (like air hoses at car shops for attaching to tools) where like an octopus, they perform the plug in and moving around of charging plugs. A company like Google or Apple (or other smaller) could employ such guy(s) to get you recharged without having to run out of meetings, skip lunch or bug others by not moving your car out of the charging station when you're full. It's really not a business idea but rather something that those larger firms should offer to keep the EV headaches down. Lost productivity to EV squabbling is much more costly than hiring some responsible lower-wage employees to help solve. You have an EV and want to be in the pool of recharged vehicles, you pay by the type of vehicle per month you have. Example rates, probably too low: Volt, $60/mo, Leaf $85/mo, Tesla $110/mo (capacity driving cost). A bay of 20 cars would bring in roughly 1700/mo, about the same as the pay for the employee. Now, we know a Volt will not always need 13 kWh. Vacation day(s)? So be it, flat rate. You are just insuring that the car is fully-charged when you leave for the day. And you are insuring that the opportunity cost of valuable employees is not leaking by having to jockey their cars or having a BEV miss a recharge because they couldn't use a station. To move your car, it could take 20 minutes. If you are a Google software engineer making $150K a year, that is a large dollar-minutes burnt. Of course, Google's motto is "we don't want our employees to leave" - it also should include "we don't want our employees to waste time".