>>96485519
>>96485164
There is a toy line called "the corps", and it includes several not so realistic looking tanks, but they are quite big. It can work, depending on your setting tho. For example:
http://www.jomitoys.com/2010/03/corps-assault-vehicle-tank.html

These (at least here in Germany) are often available for 5-10€ on ebay and other used goods sites.

Bandai and other brands have some interesting sci-fi kits besides the Mecha stuff too, pic related for example.

For Starships, you got plenty from Buzz Lightyear again, and also the "Starlink" video games included a variety of spaceships in perfect scale.