You may want to consider setting up your own 401k plan at work. Depending on your employees status (ex. mainly part-time, lots of turnover, etc.), few of them may qualify to participate. Setting it up as a safe harbor plan would minimize the testing required, so the admin cost would be lower.
The downsides would be the costs to set up & administrate and the potential for a match to your employees (although few may participate in the plan). If your husband also did some work for the shops, you both could participate in the plan and each save $18k/year ($24k/year when you turn 50). Deferring the taxes on $36k (or $48k) per year could be substantial. Also, if your marginal tax rate is 25% or lower, consider a Roth 401k, too.
If you have ton of turnover, a SEP may work as well. Here are the minimum requirements for SEP participation per the IRS:
Which employees are eligible to participate in my SEP plan?
Employees must be included in the SEP plan if they have:
** attained age 21;**
** worked for your business in at least 3 of the last 5 years;**
** received at least $600 in compensation (in 2016 and 2017) from your business for the year.**
Your plan may use less restrictive requirements, for example age 18 or three months of service, to determine which employees are eligible.
Look at your employee records and see how many, if any, would qualify.