Well, let's look at the Faberge egg: 15 of the best craftsmen in the field working for a year. If we assume that these master jewellers are pulling in the equivalent of £50000 per year then that is £750000 in labour costs for the egg in question. Since the eggs are not huge, considerably smaller than an Ostrich egg, and hollow, then even if made of pure platinum the labour costs would vastly outweigh the materials cost. Stick a retail markup on that and you're looking at over two million quid for something in the region of £5000 worth of gold and other bits and pieces, in terms of scrap value.
As previously mentioned, I treat 1gp as roughly £100, so the wholesale price of the egg in question would be 7500gp, which is in the mid-range of the top "platinum with gems" category in the DMG (p26), or at the top of the "gold with gems" category.
However, in the world of by-the-book AD&D my rule of thumb isn't relevant - there's an official pay rate for jewellers: 150gp per month. For various reasons, the rate is independent of the jeweller's skill so we don't have to worry about estimating a special rate.
Anyway, at 150gp per month we get a labour value of 27000gp for an item that has an encumbrance value of 50gp.
One caveat is that the figure of 15 craftsmen working for a year is highly dubious. The eggs (and their contents, including a clockwork elephant in one case) certainly took a year to make (and more) and 15 craftsmen may have worked on any given egg, but I doubt that all 15 worked solidly for 12 months each. What ratio to multiply these values by is anyone's guess. If we pick ½ then the DMG figure comes out at 13500gp; for ¼ it's 6750gp.
One other way of trying to translate a real-world item into game terms is the relative cost based on either average or minimum wages. This is the system I prefer, but it runs straight into the "two economies problem" discussed here and elsewhere at great length. Basically, there are "small economy" prices and wages - including the standard hirelings' prices - and there are "big economy" prices which include man of the experts, including the jeweller. For example, the jeweller's wage is 150 times that of the linkboy. If we think in terms of the linkboy being absolutely minimum survival wage of, say, £10000 per year then every jeweller in the game is on one and a half million per annum!
Which means that, if we have a relative figure for cost Vs wages then AD&D generally gives us (at least) two "reasonable" equivalent gp values.
We're told by the Beeb that the cost of one particular egg was 42⅗ times the average annual wage, and the Beeb would never lie, so that gives us another approach to looking at treasure values.
|"Maybe I'd rather have 42⅗|
strapping young tailors,
These prices too are subject to a multiplier based on how much time one feels the craftsmen actually spent out of the year on a single egg. It's pretty obvious, though, that the DMG jewellery prices are drawing on the big economy of big prices, values, and wages and not the system where every blacksmith lives in a palace (with an income in the region of £3m - although they're still wildly overpaid in the big economy too).
What has this to do with the price of gold eggs?
What this points to is that a largish gold egg (and trinket) found in a dungeon and weighing less than 5lbs can in fact be valued at thousands of gold pieces without actually being madly unreasonable. Particularly so if the treasure types are being used as a guide to what is placed.
But who is this value to? To some passing tinker the value is in the scrap - no more than 50gp. The people paying the listed price are collectors and royalty back in the big cities, not village or even town money-lenders and the like.
A great source of cash for jewels are sages - wealthy educated individuals many of whom are on the lookout for anything to do with a range of subjects from history to art and crafts. A lone nobleman's castle may produce an offer well above the scrap if the noble is a collector or has some specific interest but in the absence of the rival-offers that one might get in a city the gems and jewels will still fetch much less than the "list price". And anyone who is willing to pay top prices for jewels will also be a potential funder of expeditions to find specific items too, of course.
|"I think this one's gone off"|
So: Jewels - not necessarily just 50 encumbrance points of inexplicably high-value cash-substitute but perhaps interesting artefacts in themselves with characteristics and styles that may suggest where and who to take them to for the best price.