Who are you hosted with ?
Some web hosts include mailshot software as an installable program.
If your web host has cPanel for example, you may find PHPList in there which you can install to your web on a point and click basis.
If your host has nothing like this available but supports PHP, you could download and install PHPList yourself click here or click here
It takes a little setting up but once in place it works very well and can handle large volumes of mail directed though various filters. Basically, you can generate a message to all people subscribed to a Subaru list and send it to them and them alone. Land Rover, BMW and Honda enthusiasts would all get the message sent to their mailing group.
Your message should contain some common content as well as something group specific.