You should be able to do something like this (should work for both EF and L2SQL):
int cost = Context.Costs.Where(x => x.ordnumber == 19374911)
.Sum(y => y.linehaul + y.accessorial)) ?? 0;
VB.net should be something like this: (not tested)
Dim cost As Integer = If(Context.Costs.Where(Function(cost) cost.ordnumber = 19374911).Sum(Function(x) x.linehaul + y.accessorial)), 0)