Note that you need to log-in to see details of the bonus offer.
At the top end, you will be paying Euro 459 for 31,200 Avios (24,000 + 30%). That works out at 1.25p per Avios, based on £389. You would need to add a 3% foreign exchange fee to this price if your credit card has one.
This is cheaper than buying Avios via BAEC or avios.com, where you will pay £399 for 24,000 (1.66p). However, you must have been an Iberia Plus member for 90 days before you can transfer Avios across to BA. It is also a lot more expensive than picking up Avios points via a Tesco promotion.
The other aspect of interest is the bonus on transferring Avios to someone else (ie your partner!). This is also a poor deal, though. Transferring the maximum 24,000 Avios to someone else incurs a fee of €160. Assuming that you receive (30% x 24,000) 7,200 Avios as a bonus, you will have effectively paid €160 for them. That works out at 1.88p per Avios – very poor indeed.