Optimizing excel formula

Hello,
I have a workbook that I use to summ up the quantities of "506632" from "vulcom". Lets call 506632 part and vulcom suplier. Of course I have tens of parts and about 10 supliers. The workbook is decent in size but i've had no problems with running it untill I have created a new worksheet to see how much $ we have saved by choosing a suplier over a reference price for that part.

I am using

"{=IFERROR(INDEX(Ianuarie;MATCH(506632&"vulCom";Repere_ianuarie&Lista_furnizori_ianuarie;0);4)*INDEX(Sinteza_achizitii!$E:$Q;MATCH(506632&Data_ianuarie;Sinteza_achizitii!$E:$E&Sinteza_achizitii!$G:$G;0);VLOOKUP("Vulcom";Legenda!$H$7:$I$11;2;FALSE));0)}"

to multiply the quantity of 506632 from Vulcom that we purchased in january (ianuarie) with the price from vulcom in january. Everything works great, problem is that after populating a few hundred cells with this formula the workbook starts to slow down, opens fairly slow and every change takes time to complete.
1. do you guys have any alternative to index/match
2. do you think a macro would be faster?
thank you in advance

this is an example of what i have. Sheet 2 represents quantities of parts that i purchased, sheet 3 represents the price per meter of one part. behind those cells usually are formulas that get the price from another sheet, prices that can change each month from different supliers, different quantities and so on, but that is not important for our situation here. And on the first sheet we have the "savings". we have the part "506632", month, supliers.

SumProduct.xlsx

The standard price is set by the board, so the reference is the quantity of 506632 * standard price and savings being of course the diference beetween reference and all the others. if + we saved money if - we lost.
SumProduct.xlsx

I will have to check to see how much time it will save me, but i doubt it will make a huge difference because it's still an array formula but thank you very much for the help.