i booked a trip to Lhasa with a travel agent there in lhasa

My husband and I will be in Kathmandu on Monday the 21st of November, and we'd like to get a visa to visit Lhasa for 4 days. Will we be able to obtain it on Wednesday? we have booked flights on Thursday. we do have all the papers from the Tibetan travel agent, plus the flights and hotel in Lhasa. How much will we be charged? can we do it ourselves on wedneday in Kathmandu, without the implication of an extra Nepalese agent who is willing to charge us $220 for the two of us? it looks like a lot of money to us. what kind of visa do we need? one day visa or emergency visa? is the $220, the amount the Nepalese agent wants to charge us, right?