Speaking from my own experience, I've never purchased something I knew I wouldn't want down the road. Ultimately, writing music and being productive is fun and doesn't require a DAW to make that a reality.
I agree, the few synths I've seen under $400 that sound fantastic are the Korg Electribes... and they're actually well under $300. They can do Techno, they can do Nuskool, they can do Trance, they can do all forms of Breakbeat, and they can do Hip Hop. They can be used for Live Performance or they can be used for work in the Studio.
The EA MKII is a versatile synth for $200ish and it's filters sound amazing for the price. It is a Master of Leads, and it does a variety of Bass sounds very well. It can also do an assortment of Bleepy FX type sounds. Do me a favor and name me an Analog synth that does what the EA MKII does for $200ish... that'll be the day.
Your suggestion of Modular synths to the OP who is a complete noob in regard to owning Hardware is interesting for a couple reasons. For one, you don't even own a Modular synth, yet you talk about using such Niche hardware as if it's cheap, easy, and effective. Two, you feel you would have started with a Modular synth, that's nice: I'm sure everyone wants a second chance to do things over in life... we can all dream.
http://www.modularsynth.com/
http://www.doepfer.de/home_e.htm
Yeah, the OP can look at those pages and have a blast racking his brain trying to figure out what he needs... and in the end being frustrated.
Building a Modular Synth is for experienced Synthesists and die hard 'explorers'. The OP is new to making music so recommending such an adventure is fool hardy imho. I can respect that you wish you'd started here first, but I disagree and think this side of music is very Niche and overly complex for the newly initiated.
I as well want to build my own Modular synth someday, and have wanted to for years. The reason I haven't is because it's 'incredibly' expensive to build something that has the same amount of features as most $200 Softsynths do.
In the end, nothing sounds as fat, rich, and full as Analog; but digital emulation in both Hardware and Softsynths is good enough for 80% of the world... especially noobs.