It's documented that Jerry Goldsmith's son Joel, also a composer, helped his father on an increasing level as he got older starting in the mid-90s. IE, Joel did more and more of the detail work while Jerry did less and less of the overall themes. You can actually even hear this if you're enough of a Goldsmith aficionado and listen to various works of his from 95 onward.
As for the cheapness - I've heard a lot of recycling between DS9 and VGR myself, so I think the 'cheaper' argument may be that while they did hire a composer for each ep and record this and that, if said composer was recycling already made stuff and just re-organizing it to fit the time allotted, that would be somewhat less expensive I imagine? (Not Sure)
Though you also have to consider, I think as the 90s went on TPTB seemed to hire less variety of composers? If I'm correct in this it may have been a case of "Hire the cheapest guy the most" or something?
Look at the so-called "Visitor" suite. That famed sad theme they put on the first "Best of Trek" 30th anniv. album? It actually originated in the season 3 episode where Vedek Bariel (sp?) died, then was in "Visitor" and was re-used in the series finale. So that's one big example of recycling.