Safari snorkels for a deepender are between £100-150, cheaper ones from paddocks are around 75quid.
you could also make your own with some drainpipe, flexi-hose and sealant... there are other posts on here about how to go about it. search snorkel or raised air intake see what comes up.
over £500 is a nono. if you want, give paddocks a ring and see if they can mail one to you for an additional cost.
G