First of all, it depends what type of blood you're talikng about. Secondly you'd have to check if it's WC or CB, the latter fetching more money.
Thirdly, a female of this size would be likely to be more valuable.
Having owned one for nearly a year now, I would not recommend one for inexperienced keepers. It's definitely not a beginners snake IMO.
They can be unpredictable, some have very bad temperament and you need to have the right equipment because it's a much more delicate snake than other most common snakes. They have an issue with humidity that some may struggle to adjust to right levels, etc.
Mine has been feeding like a pig, growing a lot and we are quite happy now that she's settled very well. However we had a lot of stress in the beginning.
She's very well tempered for a blood, she's not agressive at all, she never attempted to bite, but she's extremely shy and rather not be handled, because she can panic and try to get away in a hurry.
I reckon a 5 ft blood would probably fetch something between 150 - 250 quid depending on the things I've pointed out.
That's a picture of mine: