Hi Elkwood and welcome to the GP forum. 
Pianopaul already gave some hints to very good VSTs - especially the Arturia Collection has many diffrent synths and sounds to offer. But eventually they altogehther may be a bit expensive, because you actually asked for ‘cheap’ plugins.
So i’d like to point to the VSTs from Air Music (of which i think, they really are not too bad).
I once wrote a posting about how to obtain the complete collection (which would cost 400€) for less than 100€ (on legal ways!), and this special offer still persists (excep from Vacuum now costs about 14€) - to be honest, it never seems to expire. 
Maybe it is of interest for you… read the post, follow the links and have a look at what the whole package contains…