Let me start by saying 2 thing i've learned in this buisness: Money makes abig diffrence
The more you pay for a unit (if its not areal F@#% one) will almost always be adirect indication of what you can get from it so if you wanna put money in to it i would personnly save for hardware
BUT some of those softsynths out there are damm good! professional? i would have to say very close and with agood sound card why not? the REbirth is a very sophisticated Emulation and the Rubber duck i gotten sounds just like anord lead out of it so if you got avery good soundcard to sample these softwares at ahigh bit and freq
in conclusion no you cant get away paying less if you wanna be really creative and not be stuck with the same "Engine" Sounds but its agood addon to amix or agood way to start making music just for your knowledge heres afew real nice softsynths you should check
Fruity loops
Rebirth (lots of modpacks for more sounds and drums)
Rubber duck
Stomper (Kick synth)
Simsynth (Awesome riff synth)
Audio sim(Best virtual analouge synth to my opinion works in dos though)
AXS (another classic analouge dos synth)
REeaktor (complete destruction works great with virtual midi cables and has an awesome modular engine)
VAZ modular (Amazing piece of software i would say with some FX this one Sounds Exactly like areal synth

Dt Drumstation( nice little groove software get good samples though to load in it the preset sucks bigtime)
Search for in on the web lots of record and save enabled demos for them bet youll find something for your desires
Bom,Sly-fi