Belt change costs.......

Good morning all , I think I had better start saving for the belt change on Martha . Now be gentle with me but how much or rather how hard should I be saving. Do i have to stop buying my flaggins and ciggies to fund the operation? Or is the belts something I can tackle myself (fairly basic bike knowledge but have haynes and would be alright at engineering stuff) and still allow my love and need of flaggins and ciggies. also have been told the belts need to be changed every 2 years regardless of mileage done.