Who do you use for printing postcards? Price, quality and reliability are my concerns.
I usually rotate between 4 or 5 printers. I go by the price based on the quantity. google print shops and see which is cheapest for your needs.
I’ve had great work done through expressdocs.com
I use their 5.5x8.5 full picture postcards with them doing the mailing.
My hands never touch them and the quality is A1
GT
31 cents per card printed and delivered. usps
It depends.
If I am mailing post cards (500 or more) then I use USPS.com
If it is anything less than 500 thenI use GREETING CARDS
USPS.com is a great source for cheap mailing. Can’t beat the price. Plus mail merge feature is awesome.
Now I am biased with the greeting cards because it is a service that I also sell. But the impact and customization out weighs in my opinion the yellow letter.
For business cards and letter head I use a local printer.
Use vistaprint.com, printfree.com and professorprint.com
Outsource it somewhere if you want it cheaper! 
if you are marketing too owners that are not in distress, the plain black and white post card on usps is the best way to go. For distressed owners, I would recommend something that touches thier curiosity.
Do yourself a big favor and test the plan black and white, vs the flashy stuff using two separate mailings. If they both give the same number of callers as the result, there will be no need to spend the big bucks on the flashly stuff. BTW, the flashly stuff usually just makes YOU feel better, the reciepient usually could care less.
flashy cards would make receivers say wow! black and white… well, it really depends on the person
at the end of the day, they all go in the trash. from my experience, if it looks like junk mail…
WOW makes you no money, may wins you a design award, but makes you no money. People look for content, and what is in it for them not picture on a post card.
You need to have a good strong message, not nice design. I have received good response on black & white post cards that were more than a post card. They were a sales letter on a post card. Right now I use black on yellow, it is a better color combination and I use oversized post cards not regular ones.
My post card is a 2 page sales letter printed on an oversized post card with testimonials, call to action…etc.