HMMF transmission oil by Honda is cheaper than other brands like Liquimoly and easily available. Depending on your location, I'd suggest to either buy from Honda Service centre who charge premium prices for the same stuff or go for a well reputed genuine parts supplier who charge a fair price.
In any case, getting the original thing is going to cost you a lot less than having to fix or replace the transmission due to problems with the use of non-standard oils.
Short answer, don't try to use any other type of oil than manufacturer reccommended one just because it seems expensive.
