Depending on what the DLL is doing, it may be possible to port it to MQL, probably by importing system DLLs.
Execution will be slower in MQL but maybe only a millisecond or less, depending on complexity.
However the main reason for making DLLs in expert advisors is because there have been decompilers for earlier versions of mql programs.
If we decide that porting is impossible, no payment is required.