I'm not too sure if this post will be the quality this sub demands, but comparing these two currencies (from an economic standpoint) becomes redundant due to the sheer difference in how money plays an economic role during the 1600's compared to now.

However, if you did wish to compare them, you could compare the single purchasing power of a scudo to a dollar on a commodity that we could consider as fairly constant in relative worth. For example, a sheaf of wheat, an ounce of gold, etc.

Although, it is important to consider, all commodities have fluctuated massively in value over this 400 year period and any actual ratio of worth you find between a Dollar and a Scudo will be entirely subjective and most likely wildly different dependent on which commodity you choose.

Good view on the subject: The Purchasing Power of Money, Irving Fisher, 1911

I agree with /u/Religious_Pie that these comparisons over long periods between dissimilar economies are unproductive. But I'll try to address its worth in the prices and incomes of the day.

The gold scudo was nominally 3.5g (there was also a silver scudo, but I think this came later), equal to the florin and the Venetian ducat.

One illustration of its worth is from Braudel, who estimates annual income in 1600 at 37 ducats in the city of Venice and 10 ducats in its mainland Terraferma dependency. If prices and incomes were similar in the Papal territories that scudo might last the average person ten days in the city or five weeks in its hinterland, rather less later into the century.

An alternative comparison is with England. Assuming a gold:silver value ratio of 14:1 around 1630, a gold scudo would be worth about 49g of silver or £0.44 (£1 = 111g). If English income then was around £6 a year, that might buy you three or four weeks of an average living.

Trying to convert these units into modern values is really a fruitless task. A scudo might buy you 75-80kg of grain after the bad years of the 1590s, which might make it worth $15-20 in today's money. Or it might be ten days' average GDP in a leading world economy, perhaps $1,500.

But in terms of The runaway pastor's wife by Diane Moody or Deception - a Jake Stone thriller (Both apparently $0.99 via the modern internet) my handsome gold coin - or even an infinite pouch of them - would get me precisely nowhere in 1600, because neither existed: my scudo would be quite worthless.