Titanium is definitely strong enough if the same thickness is used, and it may even be possible to go thinner.
As for the price, there is probably some where around $6 in Stainless steel in a Bushbuddy where as it would take about $20 in titanium to build one(but dont hold me to this), so the materials are not that big of a deal. The cost of a Bushbuddy IMO is in the labor, they are very well built with great attention to detail.
Working with Titanium in the thicknesses that we are talking about is not difficult at all, in some cases it is easier to work than stainless.
The one possible down side to building a BB out of titanium may be a loss of efficiency. When stainless is used in the construction of a wood burning stove it tends to hold the heat in more than other materials. This tendancy to "insulate" is why stainless is normally not used for "enclosed" word burning stoves, ie. lower heat transfer than other metals. In the case of the BB, the "insulating effect" would actually help in the gasification process. Titanium transfers heat much better than stainless and in the case of the BB Ti may actually be a detriment to the gasification process.
On second thought, after writing all that, it could be a plus to use Ti, It might help to transfer heat into the chamber where the gasification occurs. I guess some one needs to build one.