Hi it's around £200 for gastric scoping. I have heard great things about Feedmark's 'Settlex' to stop cribbing.
Some horses show lots of symptoms pointing to ulcers, such as girthiness, sensitivity around stomach area, irritability, loss of performance. Cribbing can be a symptom, but I would personally try a supplement like Settlex for a few weeks before going down the scoping route. Alot of horses lack in nutrients during/after a hard winter as they lost all their natural fresh forage and soil eating and cribbing are often a symptom. Good luck!