How long is a piece of string? There's no such thing as a 'one size fits all' plant pot.
As it's for climbing plants it would obviously need some form of trellis or support frame but other than that there's no right or wrong answer.
For safety purposes I supose you could argue that the pot, filled, should not weigh more than 20kg but you would have to work out the weight/cubic capacity of the soil to work out the optimum size. Why this isn't terribly helpful in real life is, for example, a half oak barrel has excellent depth and moisture retaining properties and is IMO an ideal wooden planter but is so heavy empty it's hard to move and when filled would take the Incredible Hulk to pick it up.
The ideal price of a plant pot is free! Again, in real life, there's no easy answer. If it is in a prominent display position price may not even be an object. For example, I would pay a lot more for a plant pot situated on my front veranda where the whole world will see it than a plant pot in the back garden where it will be less visible. Other people might take the completely opposite view and prefer to spend more money on their own visual pleasure.