Each party raised $1 billion in 2012, and before this election started, it was assumed that $1 billion each was going to be the floor, not the ceiling. They were supposed to each hit well over that number.
Clinton and the DNC still will, but Trump is saying half of that is all that is needed, while reporters are hearing he might not even get half of half of that. They assumed nearly $500m was spent in advertising in 2012, which Trump says he won't need because he gets free media. The problem is 1) that media of him is largely damaging and 2) that media is mostly for him and not downticket party members.
Trump expected the RNC to provide the money but when he got there he found out they had very little (because donors were scared during the primaries) and was expected to help raise that.
The RNC is a mess.