One way of looking at it is to consider what you would have to pay for a mileage run. At its simplest perhaps two transcons in a day so no accommodation costs or interrupted sleep. BOS-SFO and back will earn around 5000 PQMs and can be had for around $250. There are, of course, all sorts of international runs which will cost far less per mile, but you would have to factor in hotel costs (or interrupted sleep nights) and are generally very gruelling.
So, if you need 10,000 PQMs, you could set aside a couple of days and spend around $500. Or you could buy them for somewhat more. Then it comes a question of how you value your time, whether you value lifetime BIS miles and whether you value the handful of RDMs you would earn. Everyone's calculation will be different.