For a decent carcass you are looking at 450kg. This is cut into Fore (shoulder, shine etc) and Hind quarter (shin, top/sliverside. rump, sirloin, fillet etc). This works out around 500lb per side with useable being 420lb.
Are you thinking about doing this yourself (if you havent got the right gear or experience you'll end up wasting more than you could save)? Or getting a butcher to do it, it would take about 1-2 days for a butcher to bone it, prepare the cuts into how you want it and bag it up etc, so dont forget you 'll be paying for this service if you dont do it yourself.
In the 12yrs i worked in a butchers (saturday lad to full time) i never came across anyone who bought a side of beef. I used to sell sides of pork and full lambs which we prepared but not beef.