I think 4metals has done several calculations to help you decide that if you search his posts about fume hoods , scrubbers or extraction.
The cheapest way is to use a blower fed from outside your lab and use a Venturi to create the suction, part of your calculation will have to include a scrubber if your going to build one as you need the volume of air to push the fumes through the scrubber and then to be able to vent it out and away.
If you plan and lay out your complete system no doubt someone can help with your calculations so you get enough air to run it efficiently, plan well ahead so you don't have to buy more fans to run your system safely, if you can buy cheap blowers I'd be tempted to buy two, they always fail when you need them most!
