How thick are you trying to cut? The best way to laser cut is using flowing gas not sealed tubes. Most sealed tubes on Ebay are china made systems. They are disposable. You cannot refill them when the gas is depleted. You may get 6 month's out of them even if you do not use them. A well made USA sealed tube has a projected life of 10,000 work hours, but a 20w will run you 4-5k. A refill runs about 3k. I work with laser everyday. I service, repair, design, (and have a really good time frying ants from 10ft with mine). Flowing gas is the way to go and ultimately cheapest.