From personal experience, definitely pay attention to the max Polyphony the piano can support.
If it's your first piano and you buy it to start learning, then by all means go for lower price range (which are usually 64 polyphony, or lower).

However if you have been playing piano for years AND, is used to the voice produced by real piano, without 128 Polyphony it really sounds bad to your ear. In the end it actually discourage you to play on that piano because you won't be able to enjoy what you're playing.