In this case, at least the way I interpret it, "on your own", means you are on your own to find someone else to beat them with a clue stick as Eric only will do so it if you have one of their cards, perfectly understandable as his plate is full and doesn't have time (or perhaps authority) to do it on behalf of another company's product, though it may be in his/ceton's interest to contact that provider regardless on whose device they have to make it easier for the next customer.
$90 seems a little high for an install. One thing that caught my eye about the $90 fee was that seems like a fee I've seen before when someone does what the op was suggesting in taking out a cablecard from their cable box and putting it in another device. I've seen fees from $90-$120 whenever someone removes a cablecard from a company box. That may be changing as there is some "growing" pressure to make the STB install just like a cablecard install with no pre-pairing of the devices. The only thing listed at the generic metrocast site is a $2.95 monthly card rental fee... there may be more at one of the local specific sites but I didn't know what zipcode to key in. If this is in a very rural area, the fee might actually be a "delivery fee" to send a truck out with a card as some providers don't ship cards to you as well as to pick up your old box... but most providers have a somewhat local office to do this. I would have made sure to present this as a new device and not mention the other box, not sure if this is what happened or not.