The basic answer to the question is they don't "expect" anything. You give what you feel is appropriate for you. And in every church I've known access to the information as to who is giving what is extremely restricted - usually just one person - and it's not the vicar. So don't worry on that count! However ...
Bran "enough to pay wages, maintain property and do some charitable work" still amounts to a fair quantity per head of congregation.
Ask to see a copy of the accounts to give you an idea as to what's going on. Depends on your size of church and congregation. For a small church with only one salaried member of staff, this might be a guide:
Vicar's salary, pension, NI, etc., plus manse costs probably around £23k minimum. Basic bills - church heating, insurance, etc. c.£5k min. Plus - admin, youth work, Sunday school, phone, charitable work, etc. say £2k-£10k.
Even on very conservative estimates you've got £30k expenditure, which needs to be matched by income.
If you've got say 80 active members, maybe 60 households, then on average each household would need to be giving £500 per year. (A lot more than £1 a week). But obviously some couldn't afford this, some could easily afford more.