We can only go by what has already been publicly stated.
Here, SJR basically makes the case why Amorim is the guy.
At 11:24 - SJR says he has a budget in place, which could grow depending on players sold.
That takes us to 2:12 of this clip of Ornstein, who is one of the most reliable journos in the business, states that Untied are after a #9 and #10.
He also says that finances are already in place and they don't depend on European football qualification, nor on sales.
The two players he says United are focused on are Cunha (£62.5m release clause) and Delap (£30m release clause if Ipswich go down)/
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That's £92.5m on those two without needing to sell anyone or qualify for the CL.
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We also know that CL qualification would restult in up to £85m in funds, depending on how many home games are played.
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Next, we have to add up how much money might come in through sales - Rashford, Sancho, Antony, and Hojlund are the main ones (even if all aren't sold and one or two are loaned, that would still be a considerable amount of money). Then there are potential sell on fees for players like Greenwood and Carreras that might come into play + another £14m that will be saved by simply removing Eriksen and Evans' wages off the books.
Whether one has a conservative or generous estimates of how much could come in, its fair to say £100m wouldn't be unreasonable. If by chance we decide to sell one of Mainoo or Garnacho, that figure would obviously skyrocket into the £150m range.
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So back to your original question, it depends on what happens with all the scenarios above. My sense is we will buy 4 or 5 players plus Diego Leon, which could look like this.
Cunha - 62.5m
Gyokeres - 55m
Ederson - 50m
Enzo Kana Biyik - 5m
Diego Leon - 3m (already paid in winter window)
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~ £172.5m
There are obvious a lot of moving pieces at play, but if public comments by reliable sources are to be believed, then something like the above is completely realistic.