I'd probably pay £6m for him with promotion dependent add ons up to the £10m. Defence is an area that cost us last year, so we probably should be focusing a good chunk of budget there.
In fairness, £5m is more than £3m. I don't think he's worth £10m though, and we can't afford £10m on a defender so it's moot anyway. A loan with an option/obligation to buy if promoted is entirely possible though.