Just finished designing a card, but mainly because every so often I'm asked for one (other than at market). If you only want it for market customers, perhaps your email address on the label would suffice; that's what I've done up to now.
Printing is not expensive, and the outlay can be recovered if you sell at proper prices (and not in 1lb jars).
What may cost a little more is the info. you choose to include and the impression you wish to convey. If you're aiming to impress a four-year old then choose a cartoon of a smiley yellow insect and a cartooney typeface
*, but if not (and unless you're a designer) you may want to scout around for someone to do a good job.
*Did you see the typeface the BBKA chose to email to members a sober response to the recent neonicotinoid hullabaloo? Hopeless jokey font.