I also think Voyage did a lot more bottle type shows than Trek did. Many episodes took place almost entirely on the Seaview sets.
Voyage was "the ultimate bottle show." After the first year and a half, the series pretty comfortable settled into the standing sets of the Seaview and stayed there. Only very occasionally did they venture out. With the stock footage, shared props and monster costumes (not to mention episodes using the regular cast as doubles or villains), the series was apparently done pretty cheaply.