Readonly Column at run time

Hi There
I have a bit odd requirement inside a grid. What I am looking for is.
I have grid which consist of Year column and all the 12 month(July, August,….June) and total Budget amount.
This grid could have many rows for different phases of the project (Concept, Design, Construction etc)
Now my task is do the phasing for that budget at runtime.
 At run time I know which months (based on Dates Stored somewhere) I need to put the budget and based on that I have to divide this amount into these months and make all other month as read only.
I have to make sure that sum of all the month should be equal to total budget amount at client side
For example first row might be Design which might start from August and finish at October so remaining column for other months should be read only
Second row might be construction which might start from October and finish at December so remaining column for other months should be read only.
I hope this would be clear enough
Please let me know how to achieve this.
I will really appreciate that and look forward to hear from you all
Many thanks
Syed