There's no reason to assume he didn't pour a bunch of money into other systems we can't see. It's not an unobtianium powered transformer, but it's no less sophisticated than the '89 version.
You don't have to spend billions to achieve the same results. It's a car, with gadgets and a jet engine.
Batman has a car for potential car chases or any vehicular combat and that thing looks like it can be taken out easily. It may have some cool features and gadgets we have yet to see, but it looks nowhere near as sophisticated as any Batmobile before it. I get that it might be a prototype, blah blah *insert origin story reasoning*, but it looks like it didn't go far enough to be a serious vehicle for Batman. And that is just hard to excuse given how rich Bruce Wayne is.
People will probably think "Oh Bruce is just young and reckless in this film", but Alfred always has involvement so I doubt that the design is what a real Bruce Wayne and Alfred would come up with lol. It is purely in that style to fit the atmosphere the film is going for and thats about it. But the problem remains that it is not a convincing Batmobile given the money Bruce Wayne has to spend.