For flights from Bristol, start here:
http://www.bristolair...ion/destinations.aspx
By clicking on the various destinations, you'll see that many operators only have one flight per week to/from specific destinations. However some operators have two or three flights per week, enabling you to book holidays which aren't a multiple of seven days. You'll then know which websites are worth checking.
Looking through the information here shows that you'll be wasting your time looking for suitable holidays out of Exeter:
http://www.exeter-air...o.uk/all-destinations
Chris