[EDH] Best cards for use with Riku

I have a Riku of Two Reflections deck that I play casually around my college campus. The competition is pretty stiff, though: I've played against a Sen Triplets deck that ran Elesh Norn and Linvala, a Child of Alara plus Elspeth, Knight-Errant deck, and a couple other annoying ones too.

My biggest obstacle to making my deck competitive is the cost of cards I want to put in. For example, as much as I'd love to put Kiki-Jiki, Mirror Breaker or Flusterstorm in there, I can't afford it.

So, if I said that I have a budget of $20-30 to improve this deck, what cards would you suggest I put in? (The sideboard are cards I expect to receive as part of a trade; I will likely use them.)