What's the value of zero interest installments under high inflation?

Context: high inflation country. Let’s say 3% montly inflation.
A shop offers goods in monthly payments with 0% interest. For example you buy an applliance worth $100 in 12 montly payments of $8.33

How much money is saved? What would be the equivalent discount if payed up front? (Not interested in comparing with investing the money elsewhere)

I’ve tried

PV = 100 / (1 - 0.03)^12 = 144.135

I’ve also tried on an HP 12c entering:

n = 12, i=-3, PMT=100/12 and pressing PV yields -61.730

They seem ballpark accurate as yearly inflation is 36% but I’d like to know the right way to calculate it.

Thanks