Data Validation - First selection must give you a specific second selection to choose from

[CorruptWolf]

I have a attached a simple spreadsheet to illustrate what i want to achieve.

Basically I am setting up a form to work of prices for my products.
One product has many different options. Column A is the product, Column C-I is the different option for the Product.

Product is in column A, this information is easy to get to via data validation/list formula. in Block L12,

What I am trying to achieve is in M12 I want a drop down list for:
if L12 =a , I want M11 to be drop down list for Column C (a values)
if L12=b , I want M11 to be drop down list for Column D (b values)

thank you in advance for any assistance that you can offer me.

[minnesotaart]

Name each of the series of values as follows:
C2:C7 = Dropa
D2:D7 = Dropb
E2:E7 = Dropc
etc.

In B1 enter the following formula: ="Drop"&L12
In B2 enter the following formula: ="Drop"&L13
In B3 enter the following formula: ="Drop"&L14
etc.

In M12, insert a data validation with "Allow" = "List" and "Source" = "=INDIRECT(L12)" <-Don't type the quote marks.
In M13, insert a data validation with "Allow" = "List" and "Source" = "=INDIRECT(L13)" <-Don't type the quote marks.
In M14, insert a data validation with "Allow" = "List" and "Source" = "=INDIRECT(L14)" <-Don't type the quote marks.
etc.

The dropdown in column M will now refer to the appropriate named range.

Hope that helps!