At that level (20% time) there may be few advantages to accepting an employee position. It may be best for you to contract with the customer as an independent contractor. A friend of mine does this sort of work for a living in the greater Washington DC area and charges $110/hour. In general, contractors charge hourly about 2 to 3 times what a full-time salary would be including benefits, divided by 2000 hours per year. Thus, if you'd expect a full-time salary to be $80k, and about 25% on top of that in benefits, for a total of $100k, divide by 2000 to get an employee hourly rate of about $50. For a small job, you might charge $150/hour, while for a contract for tens or hundreds of hours you might go down to $100 (all numbers are for illustration purposes only and may not be appropriate for your location, experience, or exact type of work).

The pros of working as a contractor are that you're not bound by any conflict of interest or conflict of commitment issues, while you may be asked to sign an NDA (non-disclosure agreement) there should be no issues of non-competition, you get to set and change your rates as you find more work with higher-paying clients, you get to deduct your contract-work related expenses as well as e.g. expenses relating to marketing your services, equipment expenses, mileage to/from client locations, etc.

The cons are mainly that the customer can terminate the contract usually with little or no notice and for any or no reason (however, they could also fire you as an employee), and that you'd be responsible for paying the employer side of social security as well as the employee side. Make sure to figure that extra cost into your pricing.

Good luck.

The standard rate for this line of job is 5$ to 12$ per hour/8 hrs multiply into 4 weeks you will get your amount . but actually when we are offered a part time job these things never happen but some exemptions are there .But when we are approaching for a part time job the wage may be compermised to get the job

Best of luck in your job search