Here's my take on the calculations:

The official rate that LL tends to keep L$/US$ exchanges at is around US$1/L$266 (givve or take the requisite commissions)

The cost of a premium subscription is about US$9.99 a month if taken monthly, which entitles the Resident to 512sqm of mainland tier, and L$300/week in stipends.

Translated to L$ terms, that premium subscription is a few L$ shy of about L$2660/mth.

Assuming on average that each month has at least four weeks, we're talking about L$1200-1500 in stipends (more depending on the date of joining).

That leaves us with about L$1160-1460 in costs that must be covered. At L$1/10 minute we're looking at up to 14600 minutes of camping - that's around 25 days 8 hours and 20 minutes of staying perfectly still in a chair, doing nothing but talking and punching at anti-afk measures.

The time required to recoup costs from a premium subscription by camping would increase depending on the occurrence of failures to pay (I've seen this happen before either from technical issues or deliberate cc-owner malfeasance) as well as downtimes on the grid. And while you're doing this, the electricity bill and broadband fees have to be paid.

Nobody gets rich by camping. When mentoring, I do hand out a camping chair list occasionally on request... but I certainly make a fuss about it - in this manner.

You'd be better off honing your skills on WoW Rated Arena PvP and scoring a place at the next Blizzcon tournaments - you'd have more fun. Or Tabula Rasa Friday Night Fight PvP matches.

But please, oh please, spare me from the wretchedness of camping in Second Life. Really.