It's a bit tricky. Titanium welds tend to end up brittle if you're not careful. TIG is essential, as is proper weld preparation - clean with alkali or steam and then further with acetone or another organic solvent and make sure it stays that way before welding.

Assuming you're using grade 5, you'll want to weld it with a grade 4 filler rod (a pure grade as opposed to the alpha/beta alloy grade 5 / 6al-4v, slightly less strong but helps avoid weld embrittlement), with high flow argon assist gas on both sides of the material - the whole area needs to be kept flooded with argon until it cools below about 300C. The argon needs to be high purity too.

The problem is that titanium is very reactive and tends to react with oxygen and/or nitrogen in the air - the result is welds that break.

My best advice to you is to get it done somewhere with plenty of experience welding titanium - it's fairly expensive to make mistakes with. Welding lower grades is easier but they aren't particularly worth using as they don't have the advantageous mechanical properties of 6AL-4V. 6-6-2 and some other alloys are even stronger but are basically unweldable so don't even bother trying.