Unfortunately, there is unlikely to be a complete exhaustive accounting of the cost/income from the royal wedding, so we are left to gleam some information from fairly inaccurate reporting.
Even more unfortunately, this sort of breakdown usually comes from the tabloids, who are not exactly known for their accuracy. But here goes.
The Express reports that
- Reported total cost of £32M, including
- £400K Givenchy dress paid for by the bride herself
- £30M security bill picked up by taxpayers
- £90K for 20 silver plated trumpets
- £110K for flowers
- £26K for sausage rolls & tea for the 2,640 members of the public invited to watch outside the chapel (how very English!)
- Reported boost to the UK economy of £500M
The Sun has a similar breakdown
- £32M cost made up of
- £90K for 20 silver trumpets
- £50K for the wedding cake
- £110K for flowers
- £300K glass marquee hire
- £26K for sausages and tea (Such a specific amount for saussy rolls and tea!)
- £30M for security
- £300-400K for the dress
- "expected to provide a £500m boost to Britain’s economy – thanks to tourism and merchandise."
A Town and country mag article before the big day had a slightly different take, but the costs are broadly the same (it seems much of it is based on reports of Willliam & Kate's wedding 7 years prior) but once again state
Morality aside, the 2018 royal wedding is expected to provide a £500 million pound boost to the country's economy in the form of tourism, commemorative merchandise, and essentially "free advertising for Britain."
tldr; The tax payers appear to be footing the bill for security, for some pomp and ceremony and for some light refreshments for a select few "important people" on the day, and are being repaid roughly 15x by an increase in tourism and souvenir sales associated with the royal wedding.
Related: Is the British monarchy economically beneficial?