I'm a fan of the canned kesar mango puree available at Patel Bros and Fresh Farms on Devon Ave (and I'm sure elsewhere in the neighborhood). It's perfect for lassi -- I freeze the puree in ice cube trays, then blend a few cubes with yogurt and milk. The kesar variety of mango is far more aromatic than the frozen mango puree available in most groceries. It's also far cheaper; I don't recall the exact price but I'm pretty sure a 6-pack of 28oz cans is under $20. The only potential downside is that it's on the sweet side. It's fine for a lassi and probably for cocktails in which the other ingredients aren't too sweet. But it might be too sweet for other applications.