I have OOO, but I didn't install Living Economy, and I have not installed any other mods that change the barter system. Things appear to be selling at exactly the price they are worth, for both me and the vendors.

What's your mercantile?

What other mods are you running?

Are you absolutely sure you aren't running Enhanced Economy? This is exactly what Enhanced Economy does.

It also makes merchants not have unlimited gold. Other than this, the economy system works the same as it did before. Here is a mods list though

Oblivion.esm
Oscuro's_Oblivion_Overhaul.esm
Kvatch Rebuilt.esm
Unofficial Oblivion Patch.esp
UOP Vampire Aging & Face Fix.esp
Oblivion Citadel Door Fix.esp
DLCShiveringIsles.esp
Unofficial Shivering Isles Patch.esp
P1DmenuEscape.esp
Reznod_Mannequin.esp
Map Marker Overhaul.esp
Map Marker Overhaul - SI additions.esp
DLCHorseArmor.esp
DLCHorseArmor - Unofficial Patch.esp
DLCOrrery.esp
DLCOrrery - Unofficial Patch.esp
DLCVileLair.esp
DLCVileLair - Unofficial Patch.esp
DLCMehrunesRazor.esp
DLCMehrunesRazor - Unofficial Patch.esp
DLCSpellTomes.esp
DLCSpellTomes - Unofficial Patch.esp
DLCThievesDen.esp
DLCThievesDen - Unofficial Patch.esp
DLCThievesDen - Unofficial Patch - SSSB.esp
Oscuro's_Oblivion_Overhaul.esp
OOO-Map_Markers_Stock.esp
allinonebasemant.esp
Kvatch Rebuilt.esp
Kvatch Rebuilt - OOO Compatibility.esp
DLCBattlehornCastle.esp
DLCBattlehornCastle - Unofficial Patch.esp
DLCFrostcrag.esp
DLCFrostcrag - Unofficial Patch.esp
Knights.esp
Knights - Unofficial Patch.esp
The Lost Spires.esp
Harvest [Flora].esp
Harvest [Flora] - Shivering Isles.esp
Harvest [Flora] - DLCVileLair.esp
Harvest [Flora] - DLCFrostcrag.esp
P1DkeyChain.esp
Short Grass V3.esp
Toggleable Quantity Prompt.esp
Quest Award Leveller.esp
Quest Award Leveller - Battlehorn Castle.esp
Quest Award Leveller - Vile Lair.esp
Quest Award Leveller - Mehrunes Razor.esp
Quest Award Leveller - Knights of the Nine.esp
MidasSpells.esp
kuerteeAttributeAndSkillBasedDamageModifiers.esp
OOO-Level_Stock.esp
Expanded Hotkeys and Spell Delete V2a.esp

Is your OBSE installation all working okay? Keychain, menu escape and expanded hotkeys all functional?

My first guess at a culprit would be Toggleable Quantity Prompt. I've never used the mod so I have no idea if it affects the haggle bar, but if you're looking for mods to disable in your search for a conflict I would start with that, myself.

Did you ever run EE or any mod that alters barter then forget to take out all the replacers?

I don't know what EE is, so probably not.
TQP is a good guess, I'll try that.
OBSE stuff seems to be working correctly.

TQP isn't the problem, which is good, because it's a great mod.

Enhanced Economy.

Is that different than living economy?

Similar core concept, much more advanced, much more expansive.

Handles all mod added content as well, has quest engine, and loot controls.