As far as your original question, it doesn't cost anything to try some of the free soft synths which are available. Two of the ones I linked to are emulations of classic, iconic synths-- which wasn't obvious from their links:
Minimoog =
http://www.vst4free.com/free_vst.php?id=405
ARP 2600 =
http://glenstegner.com/softsynths.html
The Minimoog emulation (MinimogueVA) used to be freely downloadable from the developer's web site, but now seems to be available only through some of the free VST sites that had archived it. It's one of the virtual instruments included with Acoustica Mixcraft, which makes me wonder if that might have anything to do with why it's no longer directly available for free from the developer-- i.e., perhaps the programmer and Acoustica formed some sort of arrangement?
The first link is to over a dozen soft synths which used to be for sale from the programmer, but they were made freely available because the programmer passed away.
And Dexed (the fourth link I posted) is a free FM soft synth.
But if you have the money, and are a gigging musician, then a good hard synth is definitely preferable to lugging around a computer or laptop for playing soft synths.