Slick marketing+addictive tendencies= serious financial investment, but almost nothing compared to 20+ years ago.
As an owner of around a thousand plugs and a user of only about 20-30 I recommend you follow these steps:
1. Can you resell the plug you're considering? If so, give urself some slack in considering it. If not, try to resist. I have way too much wonderful stuff I don't use but cannot resell...
2. Some vendors like Orange Tree & the Plug in Guru Have great intro pricing and/or ridiculous sales... check first and wait if what you're thinking about falls into this category. For example, Greg at OT just had an unbelievable group buy sale on all his guitars and other awesome stuff... 50% off and more, with orange peals....
3 Find a buddy to bounce ur thoughts against... I have one. We co each other, like a couple drunks trying to stay sober... Also ask the forum at times... I put in the due date in google calendar and research till then... most things are redundant. I REGRET most of my impulse buys... many thousands of dollars worth...MANY!!!
4 Buy used if possible... reuse is good. Ask Larry... he passes on good stuff all the time!
5. If there is NO DEMO, I say forget it these days unless it is TRULY special like the Bohemian Violin/Cello, which is a landmark and turned all of the amazing folks over at VI Control upside down in a jizz freak out (I participated, wildly!)... In such cases, EXTRA due diligence is REQUIRED...
6. Get one or two amazing quality plugs instead of a sheistload of cheaper ones...within a category.
7. Many of us started where you are... we are here to help.
8. Sonar has most of what you need in the Pro Channel... great sales, killer quality.
9...lots but I'm done for now!