Don't be too hard on your local vet. The markup on brand name Metacam mostly comes from the drug company, Boehringer Ingelheim. What markup your vet does is "probably" a pretty standard markup that covers the costs involved in purchase,keeping the item in stock on the shelves so you can come in and get it immediately, costs involved in prescribing (record keeping and liability), and a reasonable profit.
Also according to most rules and regulations your vet has to abide by are established by the FDA, DEA (in cases of controlled substances) and state boards of veterinary medicine. In most cases, a DVM is REQUIRED to use or prescribe the medication that has been labeled for use in the species being treated when that medication is available.
Even though the human medication may be identical, it is an "off label" use prescribing it to a non-human and your vet might be opening him or herself to legal action either by you a federal or a state licensing agency. The same things goes for compounded medications. Those regulations have been pushed by drug companies, but they have at their heart an attempt to safeguard your animals as well as the drug company bottom line.
There are "outs" for us, but it's not quite a straight forward easy option. Some of us are a little more flexible, it seems like 37 years of practice have made me a little immune to the political junk.
Doug, DVM