A sword costs 10gp or 15gp in every D&D edition I can recall. That's a nice new 'long' sword.
Daggers tend to run around 2gp most eds - and that's a combat dagger (may even be throw-weighted), not a
simple peasant knife (1e gave separate stats for knives, d3 instead of d4). Fighting =clubs & staves are apparenly free, rather incredibly.
I find the D&D numbers are generally not *that* out of line with 1gp = $100 or £100,
1 sp a daily subsistence wage for one adult (eg a castle servant) and 5 sp a good
peasant income, enough for a farmer to support a family.
Classic Moldvay & Mentzer D&D tended to have the most plausible mundane equipment prices,
assuming a ca AD 1450 type setting - platemail 60gp, sword 10gp, set of arrows 5gp. Arrows are a bit
of a bete noire for me - IRL the arrows often cost more than the bow, but some editions give
you 20 arrows for 1gp! They should be similar to javelin cost.