Right now, it costs around $3 to send Bitcoins. But as the number of users increase, this can also go up. If you remember, during the peak of the bitcoin bull run in 2017, we had fee ranging from $30 to $50 for a single transaction. The mining pools were making a killing back then. But the strategy backfired, as the users shifted to ETH, LTC and BCH.
number of users does not affect the transaction fees but its the demand or the increase of the price , thats what trully affect the transaction fees . also , not all wallet/exchange have the same fees . some have less inexpensive fee because they use low priority or slower speed processing while others dont like waiting so they use high fees
If what you mean is free transactions and zero costs in the block chain, then everything must be free, because even the tools for mining also have an expensive price and it is impossible for everyone to be free because all of them use capital, even for themselves.
Thats impossible to happen . first of all , we need to pay for the miners so that they will process our transaction . secondly , mining hardwares are not free and wont ever be free because they are expensive and what about the shipping cost ? They will just create it and deliever it to your door step freely ? Lol .