Overhaul and TBO are really related to 1) the shop doing the
overhaul and 2) how you're using the engine.

Altho Lycoming *strongly* suggests TBO of 2000 hours and/or 12
years, whichever comes first for an O360 (for example), that's
only written in stone for Part 135 & 121. Personal use of the
aircraft (Part 91) is not mandated by TBO.

Calling around for an overhaul on the O360 I got prices from
8K-15K.