Like Old-Biscuit said the maintenance isn't much different. Yeah oil changes are more expensive because I'm buying 5 gallons of oil instead of 5 quarts, but you can go longer between changes in the DP. Where you may run into lots bigger charges are if things go wrong. Diesel engines are much more expensive to work on and parts are hugely expensive. But that is offset by the fact that diesel's are more reliable and don't break as often as gas engines.
As for is $50 enough? Only you really know that. It wouldn't be enough for me, but I tend to spend a lot of money on toys.