Our church has a reasonably sized congregation AND some very generous members. But we still struggle to break even each year. There's the upkeep of the building (heating, on-going maintenance, replacing any stolen leadworks, insurances for buildings and public liability etc etc plus other utility bills - sewage, water, electricity for lighting, costs associated with worship, like candles (they can be INCREDIBLY expensive), robes, cleaning of robes, other sundries - palm leaves for Palm Sunday service, candles and oranges for Christingle plus all other service photocopying and support.
It's one of the few buildings in a community that belongs to EVERYONE in the community, not just those who go every week, so anyone can use it (which is fantastic - all are VERY welcome) so many people who aren't 'regulars' at church may have funerals or weddings or baptisms in the building where the costs of these may be met in part or all by the Church itself (often any charges may not cover the entire costs IYSWIM). Obviously this is not a problem as the church is there FOR this and for everyone and IMO it's always lovely to have more people through the doors.
Plus the money each Parish has to send to the central Church in Canterbury (sorry - don'y know the 'official' phrases for this) which are distributed to all the works outlined in the post below. Often these are based on the number of people in the PARISH, not the congregation, so if there's a MASSIVE population in the parish and not many go to church, or can afford to donate to church, then the costs just don't add up.
Plus old stone buildings and stained glass do often need a lot of upkeep, which is not inexpensive.
Wages for all the clergy and associated staff also include the hidden costs of emploment, like the employer NI and pension costs.
But all very worthwhile. 