So ... prices ... as blacbird says, currency is mostly a classical era invention = iron age. There were also first coins in ancient egypt but they were not widely used like a real currency.
And then, definitely if you go with calling your currency "Copper-Silver-Gold", the prices may vary depending on the availability of the metals. Note that for example the old greek coins were mostly silver, of a weigth going from 0.72 gram for an obol to about 434 gram for a mine. Googling this values, I just found, that they also had a copper "chalkoi", worth 1/8 of an obol. No idea, how heavy that was.
Anyway, the romans used gold Aureus of 8,19 g worth 25 Silver Denarii of 4,55 g. Each Denarius was worth worth 4 Sesterzes, which were massive 25 to 28 g Brass coins and each of those were worth two bronze Dupondien of same size. There were other coins, two, but those values give an idea of the relative values of the diffrent metals that time and area.
Now to the value. An Obol or a Sesterz seams to be around "one day living minimum".
You can roughly try to estimate how much "work" is involved in a certain item to asume the prices and how much of his time a person of a certain profession needs to work to live at the minimum.
One Aureus is mentioned as a monthly wage for a legionary, a Denarius as a daily wokers wage - all just aproximatly and now necessary at the same time, sadly.
Slaves ... *check* Wikipedia says, in old greek times, a slave was about 3 mines which is roughly "an aweful lot" while at the same time in Gaul you got a young slave for an amphora of wine (worth only a few Drachmae (=1/100 mine) at most).
The important factors should be:
-Health and looks
-Important skills (Literate slaves are worth a lot)
-being allready whiped into obidiance (a slave that potentially runs away at the first opportunity or picks up a fight against other slaves, when put into the mines is not worth that much)
So my overall impression is that a worker in an average job, reducing his needs to a minimum can save enough money to buy a minimum-cost slave in about a month, high quality slaves should cost about 100 times as much.