not sure about the mac thing. we do postcards a little different.
I have been doing about 1500-2500 cards a week since March 1. we use a local graphic design company to design the cards, and then use gotprint.com to print. I do the everyday direct mail ( EDDM ) from the post office, and just saturate the residential walking routes that have very high home value. Strangely, you have to do larger postcards to get the lower EDDM rates, so if you go this route make sure your piece is large enough to be EDDM qualified.
we spend about 6-8 cents each on 8 1/2 x11 full color both sides postcards printed and shipped to me, and postage is 16 cents per card on EDDM. Graphic design runs me about 2-400 per postcard design, but then I reuse designs from the past as well. I try to add a few new designs every year, but this year I went a little crazy on graphic stuff. I track every sale that comes in , and postcard sales for the spring are currently running about 12x of spending on printing and postage, and graphic design. I shoot for 10x. postcards have brought us 1/2 of our sales this spring, and all the other marketing plus referrals have brought the other 1/2. So very much worth the time and expense.
I am not so sure the response/sales curve is linear however. spending more on postcards may not yield the same return. we have sent 5-6000 per week before and gotten similar sales dollars. mailing too often or to lower value properties does not yield much.
I also have tried mailing lists by income and not home dollar value /location, and thus spending 2x the amount on postage. you get the same response for the same cost, and you get bids for folks that lied about their income on some magazine survey. But you do catch some folks who live on estates out of town, so it works to do it every once in a while.
I often see web sites that "do it all" and I find they are usually not so good at graphic design, and they charge quite a bit more than the prices I pay above. I have seen anywhere from 35 cents a card to a buck a card. but then, it is easier and less time for you.