Hi, 

You may already know that when you create a Sale order, the So's pricelist is the partner's pricelist.

When you add a sale order line, an onchange is triggered and computes the new price_unit based on the quantity, the product and the SO's pricelist. 

Please kindly check the following onchange : 

@api.onchange('product_uom', 'product_uom_qty')
    def product_uom_change(self):
        if not self.product_uom or not self.product_id:
            self.price_unit = 0.0
            return
        if self.order_id.pricelist_id and self.order_id.partner_id:
            product = self.product_id.with_context(
                lang=self.order_id.partner_id.lang,
                partner=self.order_id.partner_id,
                quantity=self.product_uom_qty,
                date=self.order_id.date_order,
                pricelist=self.order_id.pricelist_id.id,
                uom=self.product_uom.id,
                fiscal_position=self.env.context.get('fiscal_position')
            )
            self.price_unit = self.env['account.tax']._fix_tax_included_price_company(self._get_display_price(product), product.taxes_id, self.tax_id, self.company_id)

Please note that also if you change the Quotation template, Odoo computes the product price_unit too based on the given SO pricelist. Please check : 
def onchange_sale_order_template_id(self) at  odoo/addons/sale_management/models/sale_order.py:66

Hope this helps. 
Best of luck.