The modern (UA) take is to strap the warhead directly on the thing, make it just as big as needed and directly fly everything into the target.
If you insist on firing guided missiles at ground targets from a drone that returns to base you're never gonna be able to compete on cost.
It really depends on the kind of war being fought.
If the cheap solution involves having troops only a dozen miles away from the enemy, then you're going to take casualties, and funeral costs are FAR more expensive then the cost to buy a large bird and fly it from a 100+ miles away.
Yeah, but you can always buy a slightly smaller bird, strap the warhead directly to it, and fly that into your target 100+ miles away.
Guided missiles specifically are insanely pricey by comparison to the warhead alone; just for the possibility that your slow, vulnerable drone might be able to return (and be used again) you have to make very expensive engineering tradeoffs, and even when the thing comes back you have to repair and service it, too (and stock it up with more expensive missiles).