According to this source, the Cassini mission costs break down as follows:

The total cost of the Cassini-Huygens mission is about $3.26 billion, including $1.4 billion for pre-launch development, $704 million for mission operations, $54 million for tracking and $422 million for the launch vehicle. The U.S. contributed $ 2.6 billion, the European Space Agency $500 million and the Italian Space Agency $160 million.

Could they have developed a good gimbal system if they had more money? Sure. However, getting more money is often a difficult proposition. There's always a risk that a project gets killed if the price goes too high. Sometimes, you have to live with the budget you can get and make tradeoffs to get the most bang for your bucks. They might have had to give up some of the instrumentation or some other less desireable trade to get the gimballed system. In the end, they went without it.