Barter For Advertising
A very cost effective way of advertising is to look for active Forums, and offer them free web hosting for a prominent banner linking to your Reseller Site or Reseller Store. Your cost for hosting their site could be as low as $5 a month, making this about the least expensive advertising option.
You set the hosting up for them (Prepaying for the year) and give them a login for the Cpanel to maintain their account. Transferring A Site to the hosting you sell is relatively simple if their current hosting also uses Cpanel. Offer to do the transfer for them and they'll perceive an even higher value plus no hassle to them.
One of the applications that the Application Installer can install in YOUR hosting account is called Revive Adserver, which will allow code for your banner ads to be placed on forums and websites. You can manage the rotation of your various advertising banners without the web needing to be modified.