about a hundered quid would be fair molly but no doubt you will be negotiated down to about �40 like my kids did. it doesnt help when your parents tell them that you only paid them a tenner.
good luck- start at 150 and let them knock you down to 50 , a tenners a tenner.
my views have always been save a third, spend a third and a third for board. i must add its always a struggle to get it out of my son tho! he is getting better i might add.