It depends on what you need. Terms, quality, volume and stuff. Check the freelance sites where you can get a quote
What is the average price it worth paying to a designer for marketing stuff like a business card?
I am for hiring professional staff. If you don't know how to do it, it will be a mess, IMO
I am not a designer but I used this service to create my company logo. This is a logo creation software with affordable price. Of course, if you feel this is not sufficient, you can try to find someone on freelance - the price will be lower than for a design company. What about the quality -you can ask for portfolios or recommendations - this is the best way to make the choice. Of course, by hiring a company you will have guarantees which I agree, matters.