update value and edit items already update on sheet by userform

Hi,
I have work on my first VBA on the attached file. I need help in couple of them. First let me tell what the sheet is all about. I have a sheet on as Item master list that has all the items used in cooking. along with price and broken down to per gram or per ml. the rest of the sheet is the menu costing sheet where items are updated using userform. Now what i want is that in the attached sheet example say on the sheet 1 the value update for "egg" is one dozen ( 12 peice ) Rs.60, which bring the value of 1 egg to Rs.5. Now what i want is if for some reason the egg price should or have gone up say Rs.80 ( 12 peice) so the value for a single has gone up by Rs.6.67. And since there are close to 45-50 sheets where eggs are used its not possible to update every sheet. what code to write so that when i update the value Rs.80 on sheet1 the result for a single peice is reflected on all the sheet where eggs are used.
Second i also want say in sheet 2 named egg nog milk used is 80 ml but that has to be 100ml. which needs to be corrected. how or what is to be added in the userform so that i can edit the information which out disturbing any other info, and also can be use in any of the sheet to correct such info.

Thanks in advance

Help me on this one

If VBA is used Every time you make changes Macro is to run to update. Instead formula is better Which gives auto correction.
IN EGGNOGG sheet in Columns F & G Formulas are given.Column F has ARRAY formula.
To enter array formula
After pasting formula
Press F2
Press Ctrl+Shift+Enter keys

thanks, it worked for me well. Wanted to check on thing, i want to lock and hide the formula in the column F & G ( i.e from F6:G35) and have this code written
Sub protectmydata()
Dim strPassword As String
Range("f6:g35").Select
Selection.Locked = True
Selection.FormulaHidden = True
strPassword = InputBox("Please Enter Password")
ActiveSheet.Protect Password:=strPassword
End Sub

The seems to lock all the cell. I am more interested in changing the value of Column D i.e when i have update the info via user form, there might be chances of editing the Column D. So how can i do that and also want to hide the formula and lock column F & G. So that it dosn't get changed by different user's.

Thanks jaslake for the help.
Since i am new and this my first macro. Wanted to check what is the code that made any value change in the Item master list, reflect the same on all the sheets ( Like egg is peice=12, dozen price =60.00, per peice=5.00 , if i change it to dozen price=80.00, per peice= 6.67 , how does the new value gets update on the sheets where egg is used )
Also why are the cell D9 and F9 not locked when the sheet is protected !!!
And is there anyway where in after entering the entire info on a sheet i want to edit the quantity part of my say i want to change it from 8 grms to 10 grms and also the respective change in pricing is also done when the quantity is changed. all this with out unlocking the sheet.

Is it possible !!

ok jaslake got it. sorry about that.
why is the cell D9 cell not locked and also F9 cell. It seems both the cells info can be typed, which can change the final pricing. And the focus seems to be set on D9 once i change the sheet.

attached excel sheet

Sorry about that. The password for ther Item master list is "edolpsgge", and the other sheets its "godspeed". :-)

Thanks,
Jolly