Quote from: sucre45 on Today at 05:20:30 PM

Who or what determines the transaction costs of a coin.

You do it. If you want your transaction to be quickly confirmed, you'll have to set a high fee, because you'll give a greater incentive to the miner. You can determine it in sat/bytes. The more inputs and outputs it has, the heavier it is and thus, the more sats you'll have to pay.

Quote from: sucre45 on Today at 05:20:30 PM

Can the developer set this himself?

The developers cannot set the fee of your transactions. However, they can set a limit (in the source code) you can't recede. For example, you cannot pay 0 sats for a transaction, because most of the nodes will reject including anything lower than 1 sat/byte into their mempool, if I remember correctly. Note that it doesn't mean they're invalid transactions; they can be normally included into a block.