There are many forms of advertising. Banner advertising if used correctly can be a great advertising tool. In order to do well with banner advertising you should have a very flashy and image rich banner design.
Different places can create the banner ads for free with a reference to their website but if you want a high quality ad I suggest you pay a small fee to have a web designer create your banner ad for you.
Banner ads are usually priced by Cost per mille (CPM) which is basically the price per thousand impressions. Start out with a small budget to see how the banner advertising is going before dedicating too much of your funds.
Find out where your competitors are advertising by going to Google and typing in the competitors site like this veteranwebdesign.com and it will list all the places that site is listed. You can use this to begin your advertising campaign.
You want your banner to catch the potential customers attention so try to get the best possible spot on a site to do that.