You can safely shoot any commercially available 38 special ammo in your M 38.
I use 158 gr hard cast SWC or 148 gr hard cast wc hand loads pretty exclusively in my M 38s.
Some folks recommend limiting +p ammo to special occasions fearing a cracked frame (a problem associated with over torking the barrel on assembly rather than hot ammo).
As a practical matter, I recommend what ever ammo you shoot best, not the sexiest high priced ammo de jur.
Without examining your revolver personally, it's hard to provide a precise value, but a range of $450 - $600 is reasonable.
Enjoy your revolver: I think it's the finest pocket revolver ever made.