There are two costs listed for each spell/item. The first is the cost in the original version and Normal Mode in Origins. The second in the cost in Origins' Easy Mode.
Inn: Restores all of your HP and MP. In the original and Origins the only way to save a game is by resting at an inn.
Sanctuary: Revives fallen characters, for a fee. If you have Life magic, use it and stay at an inn; it'll be cheaper.
Magic: see the Magic page for what each spell does and who can use it.
Equipment: see the Weapons and Armor pages for the power of each piece and who can use it.
Items: Items available in the original version and Origins.
Items (DoS/AE): Items available in Dawn of Souls and the Anniversary Edition.
Elfheim has far better equipment. After you get the ship, sail south of Cornelia to reach it, then come back to Pravoka and buy the rest of the equipment you need.
Inn: 50 Gil
Sanctuary: 80 Gil
White Magic (Level 2 - 400/250): Lamp, Silence, NulBolt, Invs1
Black Magic (Level 2 - 400/250): Ice1, Fog, Steel, Slow1
North of the large desert that is west of Onlak is a small desert. In the very middle of it is Underhill, the desert trader. Originally all he sells is the Bottled Faerie, but once you buy it he starts selling regular items.
The magic shops are hard to find. To get to them walk east, past the town walls (it will look as if you are about to exit the town). Keep heading east until you see the shops.