Hi,

I suggest you 2 or 3 diffrent ways to do that :

1. With related field : 

in res.partner class add a related field "member_price" below the field "member_type", the related field declaration should be like the following :

member_price  = fields.Float(related="member_type.price") 

2. With functions :

      2. a. Compute function :

@api.depends('member_type')
def compute_price(self):
	if self.member_type:
		self.member_price = self.member_type.price
member_price  = fields.Float(compute="compute_price")
      2. b. Onchange function :

@api.onchange('member_type')
def onchange_member_type(self):
	if self.member_type:
		self.member_price = self.member_type.price
member_price  = fields.Float('member price')

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write this on your code

@api.onchange(' member_type')

def _onchange_member_price(self):

    for rec in self:

        if rec.member_type:

            rec.member_price=rec.member_type.price                                                                                                                                                               

You should use products for that purpose, maybe together with the membership module.