As a tax payer you wouldn't overpay for anything since this has nothing to do with the bidding process.
I, and apparently most voters, don't want to pay that extra money.
Second, there is zero proof that Israel provides goods at a discount, show your work.
Third, in your fabricated scenario, a fourth company would just come in and buy the (fictitious) discounted parts and win the bid. That's how the free market works.
You're clearly not arguing in good faith, so this is the end of the conversation for me.
So if there isn't a fourth company, yes there will be a premium paid due to the boycott. Your claim is essentially that if the winning bidders don't engage in the boycott then the boycott will not have an effect. Sure, but if the winning bidder does engage in the boycott, it will have an effect on cost.