Customer discounts on effort only

We have a requirement of giving a discount to customer based on the total 

amount invoiced so far (across financial years). 
Where do we set this up? We have seen so far the discounts are calculated 
based on the value of the current invoice. 
The discount should be on a graduated scale basis for example

0 - 100000 No discount 
100000 - 200000 5% 
200000 - and above 10% 
This means that discount would only start after the customer's net sale 
value crosses 100000. 
For example, if the customer has been billed for 99000 and the current 
invoice is for 3000, a discount of 5% should be given on 2000 i.e. 100. 
Another complication is that, the discount is not based on the total amount 
billed so far, but only on the effort billed and not on reimbursements (like 
airfares, living expenses, visa charges, beeper charges etc). The discount 
applies only to the effort and not to the reimbursements. In the above 
example (invoice of 3000) say the effort billed is only 1500, the rest being 
reimbursements. The discount is only on the 500. (the rest being taken up by 
the lower limit for eligibility of 100000)

For example the customer might have been billed say 150000 so far but actual 
effort billed might be only 90000, the rest being reimbursements of actual 
costs and hence the customer is not eligible for the discount.

*The solution for this is Using rebate condition types and suitable condition 

records.

Of this to handle your first problem that is the rebate has to be applied 
only on the "effort" you have to set up a line in the pricing procedure 
which gives the rebate basis i.e the value to be used for rebate cond types. 
This I believe solves your problem of rebate only on effort.

Your second problem i.e the discount should start getting applied 
automatically when it reaches the first scale for which the values span few 
financial years. This I am not really sure whether it can be made possible 
in the invoice itself. But a work around is not giving the discount directly 
in the invoice but settling it against the rebate agreements by Credit notes 
periodically.

*Arent we looking at rebate agreeement. That appears to be a straightaway 

solution to your problem. You activate the sales organization and the 

payer for that

*I am in SAP R/3 rel.30F. 

We have 2 options to meet your requirement. 
1. Using scale in condition type ( tcode V/06 ), choose scale basis 
G.Scale based on a formula ( be: your based amount is invoice ). Define 
scale formula. You need ABAPER to define it. 
2. Using routine in Alt.calc.type ( tcode V/08 , Maintain Pricing 
Procedure ). Here, you also need ABAPER to create routine.