Well worth it if this is something you do every day, but probably not so much for a short term contract.
I use a 3M Powered Air Purifying Respirator (PAPR) system for both welding and other unhealthy tasks. It is basically a battery powered air filter you wear on your back that supplies cleaned air to a helmet. You can put in filters suited for the use in question. The slight overpressured air help keeps unfitlered air away and provides for easy breathing. Battery life typically in the 6-10 hours range. As for the helmets they come in various configurations; soft top, hard hat, with autodarkening weld screen or not, lightweight with wide visions, etc. Used just like that they provide about 2,5 times better protection than a normal gas mask. From there you can go further with a helmet that goes on to cover around your neck or add cover over your shoulders - used like that they are about 100 times more effective than a gas mask. (Well, limited by the actual filter). If you go this route it is a good idea to get a system that has helmets available for both welding and normal use.