Not really. Although I used to think so.
Every team puts the same amount in to a Bank account that the FIA can monitor.
If any team needs anything then they tell the FIA what it is and how much ect.
Now if a team turns up with a new part that has not been sanctioned by the FIA they can't race that weekend.
Very simple to do and monitor. No grey area at all.
A huge portion of costs is in designing 10 different wings and spending thousands of man hours in design and production and only bringing the final one as a new part to a race. In that sense they would only have to count the final wing but could spend 50 times what another team did coming up with that design.
The real problem with cost caps is when say Mclaren can just put 20 guys back at the factory on the pay role of a different arm of Mclaren, not the F1 arm, yet basically work through the team. Effectively you can hide costs because these companies are huge and there is no way to regulate what every man hour and every piece of material costs.
You could farm out the cost of coming up with a lighter chassis by putting most of the man hours and R&D again on another arm of Mclaren.
The big teams can push money around and effectively choose precisely how much via creative accounting to put into the team's books. The final wing and most of the R&D off the books, the final chassis, buy some materials and gift them from one part of the company to another, just have it as ordered too much so sell it at a huge subsidy to the F1 arm of Mclaren saving huge money.
You can't do a cost cap because big companies can just exceptionally easily hide spending.
They've tried to do caps via regulations because if you freeze engine R&D then the price comes down. It's not at all easy to cap costs unless you come up with some standard parts. Every team coming up with their own wheel cap system costs money, particularly when it goes wrong and they have to redesign it. If everyone had to use the same system it still costs money for teams to adapt but then they wouldn't have to keep changing to compete with each other. But how many things can you make standard before the cars are too similar, and even if you standardise simpler things like wheel caps.... the big teams will just spend that extra money on more front wing designs.
It's really difficult when it would be 100% reliant on teams being honest and including every minute of every persons time, but we already know they won't from past history.