Roads are very expensive, if you're going for the fully paved option, no matter what time period you're in.
You can figure cost as roughly :
Stone, 1' thick, 20' wide, 10' high * 2/3 (or 1/2 if you can use conscript labor like legionaires).
Multiply by 500 for a mile (a slight discount).
Half the total construction time.
This will give you a paved and graded all-weather road, with simple milestone/direction markers, and small footbridges (less than 10' long).
If you go the spell route, your materials cost will be (essentially) free, but your time is going to go up by a few orders of magnitude.
Gravel will be significantly cheaper, but will require yearly/seasonly maintenance. It may turn to mud after long (or hard rains).
Hard-packed dirt (the norm) is essentially free, and will be formed by peasants as part of their routines. It turns to mud (deep mud) after any rain.