I agree with the sentiment of your post, if not your numbers.
For example, the split of personal taxation versus corporate taxation is roughly 50/50. You don't mention corporate taxation. So, the 50,000-ish (agreed) personal taxpayers in Jersey raise about £275million per year in income tax, resulting in an average personal tax bill of £5,500 per year. The other £275million comes from business taxation (and now, GST). Sorry, but your average figures of £13,750-£18,333.33 per tax payer are wrong.
Regardless, is £550m a year right? No, of course it's not. I would like to see it trimmed to £450m. But that can't be achieved without significant public sector lay offs and a severe reduction in capital spending (pet projects).
75% of the £550m is spent in three key areas: Education (mostly salaries and grants); Health (mostly salaries and drugs) and Social Security (pensions and benefits). Where would you make cuts, given that most active voters are elderly?
The "name me one town in England" argument doesn't really work; there is no comparable town that has to run its own airport and port, financial services regulator, judiciary, legislature, etc, etc. I would like that argument to work, but it doesn't. The UK has economy of scale in many costly areas.