You have 1,000 suitcases of used notes. You have barracks crammed with conscripts. You are told to arm them with rifles. What would be the best balance between expensive cool rifles or cheap shoddy junk rifles that you can give them? The term is 'rifles'. Not guns generally, not sub machine guns nor light machine guns but rifles. You have no rifle manufacturing of your own but have an industrial economy and only some skilled and much semi skilled labour. By a miracle of coincidence you are just about to set up a small arms ammunition industry too. This awaits your choice of round.
One end of the spectrum is a fully machined walnut stocked Garand in .30-06. The other is the simplest bolt action possible with fixed sights. The Garand can only arm a fifth of your conscripts and will take much time to deliver. The simplified bolt action will arm them all fast.
Where might be the best compromise?
Have patience with me, but this scenario doesn't make a whole lot of sense. So you're buying rifles off the shelf (not manufacturing them yourself), and the Garands are being made by some incompetent manufacturer who can't make deliveries on schedule?
Historically, the M1 Garand was about as cheap as a Mauser or Springfield, maybe just a little more. The reason being that the USA IS DOMINATE and could out-manufacture literally anyone else on earth by a factor of at least 2. John Garand himself was a huge factor in making the Garand as inexpensive as it was, so really the Garand itself and its high cost effectiveness are pretty inseparable. Italy, for example, happily manufactured them for years postwar.
You could get a simpler bolt-action than a Mauser, sure, but who would want a gun that was so simple it was 20% the cost of a Mauser? It would be a miserable rifle to shoot, and it's not at all easy to see how the M1 could give your troops 5x the combat effectiveness versus that gun. Arguably, Garands already give troops several times the combat effectiveness of a Mauser or Springfield!
Maybe it's postwar and the bolt-actions are surplus - but wouldn't the Garands be surplus then, too?
It seems like you wanted to make the cost of the M1 proportional to its increase in effectiveness, but it didn't really work that way historically - and that's key to this discussion about cost effectiveness.
If it's M1 vs. bolt action, the M1 simply kicks the bolt gun's teeth in. God Bless J.C.G.
So if we're talking overall cost-effectiveness, the M1 and the StG-44 dominate the whole list. Below that are things like the MAS-36, but frankly any bolt gun is simply not a contestant. The Madsen M47 points the way here; it sold, like, two whole orders. Nobody thought bolt-actions were cost-effective by 1947, not unless they were given for free as aid, or at fire sale prices.
My personal opinion is that the MP.44 is too rough around the edges to be a very good assault rifle. I think the M1 in general would give better cost-effectiveness for a number of technical reasons. However, it would depend highly on your doctrine.
We also must consider submachine guns. Oh yes, this thread is about rifles, but we
need to talk about submachine guns nonetheless or else we're missing a good number of the lessons from WWII. The thing is, that war (especially the Eastern Front) proved that the submachine gun had enough volume of fire to make a reasonable rifle or machine gun substitute in many cases. So it's not too crazy to say "screw it, just give them PPSh-41s". This tints things a particular shade when we consider that the MP.44 is really best suited to a doctrine of massed fires - which could be accomplished perhaps even
more efficiently with submachine guns due to their low cost. Just something to think about.
So if it's just rifles, my list looks like (excluding experimentals and leaving out some guns that weren't produced in large enough numbers to make an accurate assessment):
1. M1 Garand
2. MP.44 (could be number 1 depending on doctrine)
3. MAS-44
4. MAS-36
If we include submachine guns though, slots 3-7 or so could be taken up by various types (PPSh-41 probably up top, PPS-43, Sten, M3, etc.).