LRBT's are really your best bet, one will cost about the same as a stock squad of 10 marineswithout knowing exactly what you play or what the marine army has in it, your request is rather vague.
AP 3 weapons at range,
Power Weapons in combat
NEVER take CCW's in imperial guard, its a waste of points o.e
is about all the advice I can give woth so little to work on. If you give us more details we may be able to give you more specifics.