Well, in my opinion single PC + lightwave would be
a) faster
b) cheaper
c) more energy efficient
d) more uptodate (better software, tools etc)
than render-farm of 20 Amigas.
If you have the skills to actually make money from your renders then the PC would be much more sensible investment.
@motorollin
Frankly, amiga is not very suitable for render farms, and in particular these days when a single PC can easily beat 20 amiga render farm. Just trying to give some sound advice here.