Multiply the $64 by whatever percentage you wish to mark it up. 50% would be $96.00.
Divide the $96.00 by your production rate per manhour to get your labor for your unit price. If a man can brush and roll 300 SF of drywall in a manhour then the unit price for labor only will be 96/300 or .32 just for the labor.
If you had been charging .75 per SF for material and labor (3 coats) and labor was costing you with overhead and profit, $32 per manhour (I didn't quite understand your reply) then 32/300 or .1067 X 3 = .32 meaning for the material portion of your .75 unit price, .43 is for 3 coats of material. At 300 SF per gallon you are charging about $129 per gallon for your paint to cover 300 SF, 3 coats. That comes to 43.00 a gallon average for your material.
So far we have the .43 (material selling price)
And we will take $96 (labor selling price with a 50% profit markup) /300 which is .32 then multiply that by 3 coats you have .96 per SF for the labor.
.96 + .43 = 1.39 per SF.
I guessed at your production rate and figured only $32 per manhour for labor overhead and markup. If your production rates are different or you charge more for labor after all markups then substitute your numbers for the ones used above. This didn't figure in anything for lost time due to safety meetings etc. or anything for more secretarial expenses.
Safety meetings wont cost you much if anything at all. The benefits gained will far outweigh the 10 minutes per week or so that it takes for a toolbox talk.