それでは、このお金をあげるから、おじさんにカメを売っておくれ
What does おくれ mean in this context? What is this verb form?
「くれ」 is the imperative form of 「くれる」 and the 「お」 is the honorific.
「Verb in te-form + おくれ」 = "Do ~~ for me / to me."
Without the 「お」, it would sound much less friendly.
「おくれ」 is used much more often in fiction than in real life -- at least in real, present-day life.
"Now, I'll give you this money; (Please) sell me the turtle."