Best cheap or free arpeggiator ?

[speccyteccy]

ARPocalypse

Not really.
The website says:
"Despite it’s name, ARPocalypse is not an arpegiator. ARPocalypse is a 8 step rhythmic pattern generator. Simply put it takes chords of up to six notes and plays them in a predefined sequence in sync with your sequencer."

Well, I guess some arpegiators take a single note and play a predefined chord, but ARPocalypse does most of what I always thought a normal arpegiator does and a whole lot more:

Custom note order (not just up / down etc.)
Per note velocites
Per note gate
Per note legato
Per note swing