Seber Cart can be configured to use flat rate shipping (same freight cost regardless of quantity or cost).  To do this we need trick Seber Cart a little into giving us the result we want.  Do the following:

• Log in to Joomla administrator and select Components->Seber Cart->Configuration
• Under Shipping set the Calulation Method to Freight Table (QTY)
• Click on the Save button and now select Components->Seber Cart->Freight Table
• Make sure you have no entries listed on the page (delete any that already exist)
• Click on the New button
• Set the Start Number to 1
• Set the End number to a very high number. 999999999 should be enough
• Set the Shipping Cost to your flat rate,  Click on Save.