The gate receipts used to get split 3 ways years ago. The 2 teams and the FA getting a third each after expenses. I think it's changed since then and I think Rexn said what happens now but it escapes me.
The current format varies by round. From gate receipts, costs are deducted, including visitors' travel costs, policing, stewards etc.
Up to 3rd round, equal split between clubs.
3rd-6th rounds, 45% each to the two clubs, 10% to pool. On replays, 42.5% each to clubs, 5% to FA and 10% to pool.
It gets more interesting. If a non-league club is involved, the split changes, non-league club 50%, league club 40%, replays is 47.5% and 37.5%.
TV money is around £150k with about half that for replays. and increases after round 6.
For a non-league or lower league club, gate receipts can be hugely significant. One of my golf mates is Director for a League 1 club that had a run a couple of years ago with that setting up training facilities and other investments for years to come, also affecting not selling their best players and able to compete in attracting younger players. Having said that, it is a fraction of the annual wage for an average Premier League player.