There are exhaust flexi sections available on Ebay for £20-25. How easy, or otherwise, is it to replace this section? 

For the sake of keeping information on the forum; I had mine refitted since mine was welded into place, by an unskilled welder. I assume it could be clamped as well?

The job itself is easy on paper. The only really issue is undoing the various fixings and clamp to the middle section if they are very rusty. 
 

I clean them all up with a wire wheel on a drill and soak them in some GT85 or similar 10 minutes before trying to undo them. 
 

You may find this still doesn’t work, in which case applying heat to them should work. Worst case, you’ll have to cut them off.