Spread
Paid on every entry as the gap between bid and ask. Multiply typical spread by pip value by monthly lots to get the monthly figure.
Commission
Charged per lot on raw-spread accounts, usually round-turn. Compare account types by adding commission to the raw spread and putting the result next to the standard account spread.
Swap
Charged or credited every night a position stays open, with a triple charge on one weekday to cover the weekend. On multi-day trades this frequently exceeds every other cost combined.
Slippage
The difference between the price you expected and the price you received. It is not a fee, but it behaves like one over a large sample, particularly for market orders placed around news.
Working out your real number
Take last month's trade history: total lots traded, average holding time and number of nights held. Apply the four costs above. The result is what your strategy must beat before it earns anything.