With postcards mailed to nice areas I usually make $5 for every $1 spent. With everything else YP, newspapers I always broke even, but if you do a good job they all pay off in the long run in the form of repeats and referrals, but why spend $90 to gain a customer when you can spend $30 or less.
Also keep in mind that your return will get better each time you mail to an area. Instead of hitting 60,000 homes it is better to hit 20,000 homes 3 times.
If you don't have a website I would also invest there. I now pay $9.95 a month for 10-15 new customers a month.