If you want a super light weight chassis, look to the bicycle tubing suppliers, like Prestige, Cinelli, Reynolds, etc. You can get air hardening double butted alloy steel tubes with strength in the 170-180 ksi range with decent enlongation. The fabrication techniques are not that bad, some tubes are suitable for TIG welding, some for lug construction, some for fillet brazing.
Any way you do it, it's a lot of work for only a small ammount of weight saved.
The only thing that makes sense to me is a carbon fiber monocoque construction (vaccume bagged with a foam or honeycomb core of course). You can make a tremendously strong structure with incredible stiffness and light weight also. The materials are not as expensive as titanium tubing, but the cost of molds and layup supplies will make it expensive for one piece. Production of several parts can make the cost reasonable.