All the times I have had 2 stage vettings done the horses have also been lunged to check lungs etc. I have asked for this, but it's never cost me any extra.
If you want to insure the horse though for more than £3k or £5k you will need a 5 stage vetting. Depends on insurance company they have different thresholds
Also normaly take blood sample oh and scan for mircochips. Its not normaly much more for five stage though. And you can sometimes pay more for teeth exam too.