alan, i think i understand your figures, so as loose eg.
10ph x 100h = £1000=add paid
but your time is 100hours with no pay so i would think that nearer the 250 hours is your break even figure cos extra 150 hours at 10 = £1500 . devide total time of 250h by cash left after add (£1500/250=£6.00 ph cash return, plus of course you have an advert paid for.
that does seem like alot of work to do to break even
as people often think companies with big ads are expensive, maybe consider a smaller simple add with an inclusion (hook) like " mention this add for our special promotion rates". the more personal type of add?
i dont know, but maybe your promotion could be 10%disc on over 3 hours per week for domestic work tell em how much it would work out saving per month! so £10x3= £30 less 10%= £3per week x 4.333 (weeks in the month) = £12.99 saving per calender month, or £155.88 per year!
people do go for things like that, and when they call you just need to "sell" them your services!
i view the add as a tool to get the calls not sell the service, thats my job if you know what i mean.
regards,
steve
ps. sorry if this is the old sucking eggs for you, its just my thoughts as i have a sales and finance background, i obviously dont know what your background is. maybe if nothing else food for thought!