what is the cost per day for every US military personnel?

By "every military personnel" do you mean active duty, reserves (not
including individual ready reserves which are basically no charge
except for a pittance of paperwork), Coast Guard (Department of
Transportation but receives materiel support from the Navy), National
Guard (quasi-federal), retirees, and civilian military employees (hoo
boy, lots of categories for them)? How about the military exchanges
which receive support from the military (and have military members
overseeing operations) but are essentially private companies?
Similarly, military commissaries are pretty much military operations
but have huge areas that are civilian operated.

Just trying to make it easier for a Researcher as well as point out
how what seems to be a simple question can be hideously convoluted.

Here are some 2006 numbers from the DOD Annual Report to the President
and Congress:

Military Personel: $111B
Operation & Maintenence: $148B
Military Housing: $4B
Military Construction: $8B
Military Endstrength: 1.2M
http://www.defenselink.mil/execsec/adr2005.pdf

All the military personel and military housing $$ should be counted. 
I'll estimate that 67% of O&M, and 50% of military construction should
be counted towards the cost of military personel.
The total cost of the 1.2M personel is $218B with my estimations. 
That is $182,000 per person per year... which is about $500 per day if
you count every day of the year, or $728 per day if you assume they
work an average of 250 days a year.