there are too many details unknown:
1.) is this your only source of income?
2.) what was the arrangement with the prior guy?
The prior guy could have been getting some paltry 2-3K per month sum to just baby sit the lab, in which case run. Or he could have been an employee with full benefits and a pension.
I would personally shoot the moon if this is all you got on the burners. Would try for 300K.