Is it still legal to....

Boyd,
Here's how I get a lot of my ad out in my local area. (I don't have lots of money for expensive ads):
On my word processor, I format a standard size piece of paper into 3 equal sections. I then design an ad on one of the thirds and simply duplicate that ad onto the other 2 thirds of the page. I then have my local printer run off 1,000 copies and then cut the copies into the 3 separate sections (they have a special machine that does this neatly). The total cost with my printer for this is $40. That gives me a total of 3,000 ads, which are each 1/3 of a regular sheet of paper.
I have a girl that works for me, that I got by having the "Career Center" at the local high school in my area post a help wanted flyer for free. I pay her $8 / hour to ride around in the passenger side of my car and tape my 1/3 page ads to mailbox posts. It's illegal to put ads in or anywhere on the mailbox itself, because of US postal regulations.
Doing it this way, I'm able to distribute about 150 pieces per hour. Here's exactly what the costs work out to
Cost of each piece: $0.013
Cost of Distributing
each piece at 150 pieces
per hour: $8 divided by 150 = $0.053
Total: $0.066 (Less than 7 cents each)

I make five times on my investment whenever I do a distribution like this. Of course, it depends on the strength of your offer and your ad copy. You could also distribute the pieces yourself, but you'd have to do it by foot, since the mailbox is on the passenger side of the car. I highly discourage you from driving on the opposite side of the road to do a distribution by yourself in your car, because a cop will give you a ticket if they see you, and it's just not worth the fine and the points on your license, plus it's dangerous.
I tried staying on the normal side of the road, doing this myself, and using a long stick to get the flyer on the mailbox post, but this took too long, and people got mad when they saw me swinging a stick out my car, near their mailbox. Your best bet is to go through your local high school or church to hire a kid for $7-$8 an hour to sit on the passenger side and put the flyers on the mailbox posts. You should be able to get 2-3 flyers on each post every minute. Good luck!
Joe