Falcon XH panel van. Starter motor?. My reliable old workhorse wont start last week i had to start it with jumper leads but was

My reliable old workhorse wont start.
Last week I had to start it with jumper leads, but was puzzled as the battery was fully charged.
This morning i tried to start it after a week of sitting on the drive and and it made a real crook ticking noise.
Now its not doing a thing.
Anyone else had the same problem!
if it does need a new starter motor, how much much would i be looking at to replace!