(all of this is true for by-the-book B/X; applicability to other editions may vary)
A potion of treasure finding (Cook/Marsh X48) tells you the direction and distance of the largest treasure within 360' (unless blocked by lead). I would assume that most normal dungeons have a radius of less than 360' so that's a good thing to have handy. The effect lasts for 1-2 hours.
And…. an Alchemist (Cook/Marsh X21) "if given the formula or a sample, an alchemist may make a potion at half the normal time and cost. They may also conduct research into different types of ptions at twice the cost and time required for a magic-user."
Under the rules for producing magic items, X51, a one-shot magic item costs $500 x level, and takes 1 week x level of the effect. A potion of treasure-finding is pretty good stuff: it's notably better than the second-circle spell locate object. I'd put it around third-circle. This means it would cost around $1500 and three weeks on a DIY basis. If the alchemist had a sample to work from, that would be $750 and 10 days; but even if the alchemist had to research it from scratch that'd be $3000 and six weeks, plus $1500 for his monthly fee, for a total of $4500. A significant sum, but by the time you're at Expert level it's not outrageous.
If you were going after a really large hoard, in a really scary dungeon, and you just wanted to get in and get out quickly (i.e., making a Raid on the Pharaoh's Tomb or Scather's lair), it would be a very wise investment.