Ummm, let's see. Cost depends mostly on who you buy from, what quality you're looking for, and who you buy from
For instance, most of the llamas on Tim's parents farm will sell for about $500-1000 CDN. That's because most of them are "pet quality". Their fibre isn't competitive enough to demand much more, and while most of them are just halter and people trained (meaning, you can take them for walks and people and loud noises won't bother them), there are a few that are better trained, for like packing and driving. Those ones will cost more. If they are just halter trained and people trained, then they likely won't sell for much more than $500.
Now, there are some llamas that have EXCELLENT fibre, good enough to rival that of an alpaca (which, personally, that's all alpacas are good for. I usually compare alpacas to sheep -- they tend to sort of operate on a collective conscious mind and do really stupid stuff and freak out at the littlest things. However, that's not to say they are all like that, nor that they can't be trained -- it's just difficult to work with them). Those ones are super expensive. In Canada, llamas tend to go for less than in the states -- even the show champions are cheaper in Canada.
I've heard of just a breeding to one of the top US males going for over $10,000 USD.
Your best bet is to find a hobby breeder and either get a young one (just weaned) and train it yourself (as there are some techniques that are different with every trainer), or get a youngish one that still is trainable.
Llamas live to be about 15-20 some odd years. Some of the ones on the farm are over 9 years old now, and those ones tend to be fairly stubborn!
Llamas take really well to voice commands. One of the driving llamas on the farm -- if he's on a good day, and not too tired (as he's 12 years old this year) --- you can walk him around by using voice commands as long as his halter is on. Leave the lead rope on his back and he'll do what you say!