Ancients are almost always cheapest from specialist dealers . I talk about buying on the web below, but I recommend you do not skip down to it. Read the next part about specialist dealers first. I used to visit dealers in U.S. coins hoping to find an occasional ancient coin at a good price, but I spent far more in gas driving to see junk than I ever saved with a good deal. It plays a role, but is often misrepresented.
Condition is the tricky one.
The same ruler in the same denomination can cost 10 or 100 times as much in super grade as in very worn or corroded condition. Use catalogs to learn about how the clarity of the remaining design details relates to price. Doug Smith has an excellent webpage illustrating the factors that affect condition . However, his grades are what the better dealers use. Grading is very contentious and you must be careful not to keep coins that are worse than the description led you to expect.