Through the built in uMail you can send any file which is or 99mb or lesser, however with packet forwarding feature you can host any service on utopia (websites,file server etc) which won't have any limitations aswell. As network matures the built in file limit may increase aswell ...

There is no fee to use Utopia , but for registering NFT's etc inside Utopia like uNS which are used for packet forwarding or hosting websites that require a fee , I have shared a screencap of the network fee
https://img.drhack.net/di/5UXH/fee_structure_utopia.png