I use Shimano Mtn Bike clipless (about $55.00) on my road bike. Work great. I use traditional toe clips on my other road bike and my "scoot about town" mtn bike. You can also walk on just about any surface with mtn bike clipless and shoes.
I have no problem interchanging between the toe clips and the clipless - none at all. I can also use just the plain platforms my wife has on her bikes.
The Shimano are less expensive and work really well.
I use SPD sandals with the clipless, and also have a pair of mtn bike shoes which I used to use with the clipless. But, I haven't worn them at all since I got the SPD sandals.
I love clipless - makes me feel as if the bike and I are joined into a single unconquerable machine!
I fell 2 times in 1999 getting used to the clipless, and none since. I ride about 3,500 miles per year or so.