What is the command policy or AR reference to leadership forcing soldiers to spend money?

4 haircuts a month at $10 (?) a pop...good looking out for your fellow soldier but maybe his finances need to be looked at closer if $40 is threatening him with bankruptcy.

There is no AR cite for something that does not exist.
You can find no AR paragraph that forbids a commander from requiring an SM to buy a baby zebra.
Ar670-1 Male Hair
(2) Male haircuts. The hair on top of the head must be neatly groomed. The length and bulk of the hair may not be excessive or present a ragged, unkempt, or extreme appearance. The hair must present a tapered appearance. A tapered appearance is one where the outline of the Soldier’s hair conforms to the shape of the head (see scalp line in figure 3–1), curving inward to the natural termination point at the base of the neck. When the hair is combed, it will not fall over the ears or eyebrows, or touch the collar, except for the closely cut hair at the back of the neck. The block-cut fullness in the back is permitted to a moderate degree, as long as the tapered look is maintained. Males are not authorized to wear braids, cornrows, or dreadlocks (unkempt, twisted, matted, individual parts of hair) while in uniform, or in civilian clothes on duty. Haircuts with a single, untapered patch of hair on the top of the head (not consistent with natural hair loss) are considered eccentric and are not authorized. Examples include, but are not limited to, when the head is shaved around a strip of hair down the center of the head (mohawk), around a u-shaped hair area (horseshoe), or around a patch of hair on the front top of the head (tear drop). Hair that is completely shaved or trimmed closely to the scalp is authorized. (See figs 3–1 and 3–2.)

Now specifically "The hair on top of the head must be neatly groomed. The length and bulk of the hair may not be excessive or present a ragged, unkempt, or extreme appearance"
You will not find the words " neatly groomed" , "excessive " "present a ragged, unkempt, or extreme appearance" Defined in the AR, there fore they mean what the reader interprets them to mean.
If the reader interprets "The length and bulk of the hair may not be excessive or present a ragged, unkempt, or extreme appearance" to require a weekly hair cut to comply... then thats what it takes.
You may disagree, bring the issue to the COC, if that does not resolve the issue, go see IG, they will investigate and advise the CDR.. be advised they can not ORDER the CDR to do anything... only a more senior CDR can do that...

SPC (Join to see) "I'm trying to figure out how this can be avoided so he doesn't go broke."

Well Im trying to figure out how getting a hair cut weekly (something I did for 28 years 7 months E-1 to E9) is cause your friend to go broke.. I call BS.
And if this friend has truly mismanaged his finances so bad that he can not afford a weekly haircut... Buy a pair of clippers and cut his own hair or have a buddy do it. One time expenditure of $30 and no more spending $9 weekly to get a hair cut.

When I was in, it was a rare thing indeed that you did not have a barracks barber or 8 within the unit. sometimes you paid him with a beer, but usually in a tight knit unit, others would see this, and he would give you the hookup and keep you taken care of. In fact the only time I actually went to the post barber was for my promotion board, and my PSG sprung for that (his own personal policy for soldiers going to the boards)