Well before you dump a bunch of money into your daughters larp gear, you should probably specify where she is playing, and then ask those people what gear she might need.
>How would you recommend getting into LARP?
By going to a larp near you. Literally any larp.
> What is it really like?
Fun. Past that it depends on what kind of larp you go to
>And what's the starting costs?
Anywhere from $0 - $infinity.