Well, what effects, specifically, are you looking for? There are so many good to great, free to inexpensive plugins out there that I would only get a UA plugin if it's precisely what you want. Some examples:
For analysis, dynamic range, and some EQ, I use open source plugins (MAnalyzer and MEQ are great)
For checking phase on my mixes, I use an open source plugin (I forget the name off the top of my head)
For tape saturation, I use an open source Plugin (Tesla SE)
For tape emulation, I use Waves Kramer Master Tape
For compression, I use the SoundToys DevilLoc or Waves Kramer Pi comps
For limiting, I use the Waves OneKnob brickwall limiter
For 90% of my EQ and reverb, I use Cubase's plugins; I also use Cubase's soft synths 90% of the time
What I use my UA for: Pultec EQs, pretty much. And that is only for flavour/colour, not for correction.