I'm looking to buy a commuter bike. I've seen the type that fold up but they come with smaller wheels (18) than type a regular bike would use. How much more peddling and work will I have to do in order to get around?
Hm. 18 wheels are very uncommon. Are you sure they aren't 16 or 20? If your commute is long, get the bike with 26 wheels. This isn't to say that you should buy a cheap bike with 26 wheels in place of a good bike with 18 wheels. Bikes with 18 wheels accelerate and handle faster than those with bigger wheels but the inertia to carry you forward is a lot less.
How many pointed sticks can you find?
It all depends on the gearing my friend. You can gear a bike with 16 wheels to cover just as much ground as a bike with 29 wheels. Example, I have a buddy that races go-carts. His go cart has 9 wheels and can hit speeds of 120mph with a small displacement engine. it's all in the gears.
The difference is effort required is small to none. The main difference is in how the bike feels (and ability to handle obstacles on the road). The gearing is quite different on smaller wheeled bikes, but the small wheels have less air resistance (and in theory can be lighter) so that more or less offsets any rolling resistance differences. I can tell you from experience trying to stay with a strong rider on a Moulton --- and usually getting dropped --- that small wheels do not necessarily make for a slow bike. Have a look at the video at the link of John Howard's world speed record (152 mph) on a small wheel bike in 1985.
