I few things I do:-as a girl, I wear a nice-fitting golf shirt, pants, and running shoes (in case I need to run...seriously)-I go Saturday or Sundays during the day-stand at a 45 degree angle from the door, so if they see you through the window, you don't look intimidating. 

Only thing it cost me was the paper, envelopes and some stamps.

Yellow letters when done correctly (targeted list, hand addressed, first class stamp) usually produces at least a 5% response.

They didn't have regular stamps either.  

and get off the phone to conserve your time.....take them off your list and don't waste any more stamps.....but don't trash the prospect unless they tell you to.

Also on a standard stamped postcard they don't get returned so keep that in mind. 

Did you pay for the postage stamp?  

@David Hartoon Buy a pack of post postcards from the dollar store, it doesn't matter what they say, smaller than 4.25"x6", apply a first class stamp for postcards, .34¢, and write on the PC, below the stamp, "Forward Address Requested".

For us the only place we can buy stamps, since we buy in rolls of 10,000, is from our distribution center which is also our main Post Office location.

or is the cost per stamp something I just need to get use to spending?