It's common in written English, including some literature, that seeks to represent colloquial spoken English to use would of instead of would've. This usage is at least 80 years old, probably older.
For instance, the book The 42nd Parallel (published in 1930) by author John Dos Passos contains this line:
"I would of too if I hadn't gotten sick."
This is not a spelling mistake. This is a deliberate spelling to represent colloquial speech.
Nowadays, many native speakers mistakenly write would of instead of would've simply because they don't realize that that is the correct way to write the contraction of would have.
To hear tell of is a usage that goes way back to old English and represents the ellipsis (omission) of such a noun or pronoun as 'people', 'persons', or 'someone' before the bare infinitive tell, say, talk, speak. It is now dialectal or colloquial.
Source: Oxford English Dictionary (OED).
An example from about 1325:
King Macolom hurde telle þerof in scotlonde.
In modern English this would be heard tell (there)of.
Before it be two days, if they do not send us other orders, they will hear tell of our having done something.
Note that the most common preposition used after tell, etc is of. The writers may have changed it to 'bout to avoid repetition.
So the clause is equivalent to
...you might've heard [people] tell about the price on her head.
You can also look up hear tell in many dictionaries, such as Collins.
The legal term hearsay comes from this old usage of hear + people + say. See Etymology online and the OED.