Laser tubes have a use and no use shelf life and can be rather pricey to replace. If you only plan to cut now and then may consider just using the online shops to do the cutting for you
+1 to Charley's comment: I have had a number of hulls cut by http://www.foxlite.com/ along with ABS parts. For the cost and quality, there is no way I could ever justify my own laser. Even for one off's of a full hull kit for a large BB, the prototype never exceeded ~$160 including setup fee. Unless you plan on doing a ton of one off parts that you can not combine into a single larger order, it will take a long time and a lot of effort to beat them.