Hi,
Simple IRA is one of the least expensive for you. This year I think the employee can put in $10,500 of their salary tax deferred and then you can match 3% of their gross at the end of the year. In my opinion if they want to save for retirment they have to save something to get something.
If you want to be very generous a SEP IRA will let you and them put in a lot more money but whatever you do for yourself you need to do it for them. I think I put in 15% of gross and they put in nothing up to $27,500 per year a few years ago.
401K is no practical as it is very expensive for.
Lots of info on the web if you google SEP and IMPLE IRA's
Good Luck