PM Netanyahu raised the issues of purchasing an airplane for official trips by the PM and president, and building a new office and official residence for the Prime Minister. The cabinet wasn't to discuss whether or not to approve these expenditures, but rather whether or not a public committee should even discuss if they would be cost-effective.
Yair Lapid objected to the proposal, claiming that "in these days of tightening the belt and raising taxes, as the gaps between rich and poor are among the highest in the world, it is appropriate that the Israeli government demonstrates austerity and does not make decisions that would lead the public to feel like its leadership is disconnected from everyday hardship of citizens."
(Side point - Lapid recently cancelled his planned tax increase, so I'm not really sure what he means by "raising taxes".)
According to Lapid, in the past, experts have looked into the option of purchasing an official government plane, but have found that it would increase expenses. By how much and for how long? Lapid didn't mention.
According to the Jerusalem Post, the Finance Ministry (which Lapid heads) calculates that despite the 100 million shekel price tag, and 5 million shekel per year in maintenance expenses that would come with ownership of an official plane, the purchase would pay for itself within five years (by offsetting the costs of flights currently paid to airlines, and within 10 years, the government would be saving 12 million shekel per year.
Despite this, Lapid objects to merely forming a public committee to look into the matter. Odd, given that there are likely only two possible results - the committee will find that the government can save money, in which case it will recommend buying a plane and saving money (saving money = good), or the committee will find that buying a plane will cost more than the way the government currently funds the PM's trips abroad, in which case it will recommend to not buy a plane (not buying a plane = what Lapid seems to favor). Either way,
Lapid's position, apparently, is that saving money is not a good idea if it looks bad. The symbolism of tightening the government's proverbial belt, even though it will otherwise spend more money on flights, is apparently worth 12 million shekel of taxpayers' money.
Of course, from Lapid's point of view, objecting to the very idea of a government plane, no matter how much money the government (and thus the taxpayers) will eventually save, makes perfect sense. Purchasing a plane saves money in the long run, but will be a financial liability for five years. In other words, buying a plane now will be a financial burden during Lapid's tenure, while the next Finance Minister will enjoy the savings. Lapid's objection seems to be more of the same petty politics he has always said he is above.