Well I cut and packed 7 deer, so at a retail value of £400 apiece or thereabouts the £300 labour doesn't sound so bad.To be fair (to you), it's not really that wonderful. You're saying 15 hours cutting, probably knock an hour and a half off for breaks etc., so your labour would be say £300, then add in electric and waste disposal costs, the only reason you have for doing it is you enjoy being your own boss.
(But yes, you're right, the real reason is that I enjoy doing it. That's the basis for all my business decisions).