Sorcerous Occupations and Services
I am by no means an expert in economics, but I have consulted with my friends on this topic and got different ideas. It seems that it would be difficult to gauge the effects of magic on economy and estimate a sorcerer's monthly pay. Spells rarely create permanent effects. If the spells produce something material, they need resources. Magic requires a lot more character points, and hence time to learn, so mages would expect to earn more than mundane specialists (for example, GURPS Thaumatology - Sorcery assumes that in a world where enchanters are as common as any other highly qualified professionals, enchanters are expected to have Comfortable wealth level). Spells rarely require a long time to cast, that's a major advantage of magic.
Let's say that a sorcerer has a 8-hour workday. Most spells cost 1 FP to cast, and FP is normally recovered at a rate of 1 FP per 10 minutes of rest. Let's assume that it takes 5 minutes for the customer/client to explain what he wants to be done. Casting time is neglected, as it is often only 1 second. Thus, the caster can optimally serve 4 clients per hour (5 minutes to receive the order and talk about the details, 10 minutes to replenish FP spent). This means that the caster will be casting spells 32 times per day. Since there are 22 workdays in a typical month, each casting is worth (Comfortable monthly pay) / (32*22). For a TL3 setting that would be $1,400 / 704 ≈ $2. Unless the caster's service are vital to the customers, it is unlikely that he will be serving clients constantly. I suggest doubling this casting cost to reflect that. Thus, a 1 FP/1 second spell costs $4 at TL3 for a moderate-demand job.
Many sorcerous spells have no casting rolls. In this case, the job roll usually is made against IQ or an appropriate skill for the job in question, modified with Talent in both cases. I suggest treating a casting job as a freelance job with flexible income as described on p. B516.
These calculations assume that spells cost 1 FP. If your Sorcery or Magic as Powers system has variable FP costs, adjust monetary casting costs accordingly simply multiplying the 1 FP cost by the actual FP casting cost.
Another assumption was that the casting takes an insignificant amount of time. Control (pp. P90-92) implies that creating something beautiful and functional requires the same amount of time as normal and requires an appropriate skill roll. In this case, the sorcerer differs from his mundane peers by the lack of need for tools. Typically, he is still limited to discrete objects made of the same material, so it's safe to assume that a caster of that type would earn just as much as a mundane professional.
If such sorcerous professionals exist in the game world, then magic guilds are as likely to exist. Such guilds will set service prices, require sorcerous professionals to pay fees, and regulate the trade in other ways, for example, via racketeering. In such regulated societies, I'd suggest basing the casting cost off the spell's full character point cost. For example, full character point cost * monthly pay modifier. Thus, if a TL3 guild lets its low-ranking members cast Detect Magic (7 points) and keeps them at a Comfortable level, then the casting cost would be 7 * 2 = $14. A downside of this method of pricing would be that point-expensive spells, such as Resurrection, will still cost not that much.