Ditto on the cleaning; the best spider deterrent is daily vacuuming, especially BR's because they are so reclusive and they are nesters, not webbers. They sell BR traps, but they are nothing more than a sticky patch that will catch anything that walks on it, and nothing that doesn't.
I have, however, had success in deterring spiders using garlic. We were infested with all sorts, and one that I found was so big I heard it thump down the stairs.
So I was trying to find a natural spray or herb to scare them off, when I remembered that in the Middle East (where I was born) nomadic peoples use garlic in their bedrolls to ward off scorpions. Scorpions and spiders are both arachnids, so I googled "Garlic spiders" and got a bunch of recipes - how gross is that?! But I tried it, and it worked! I cut garlic cloves in half and put them in the corners of the rooms and the problem was dramatically better. I had to replace them every week or two, but it was natural, safe, cheap and effective. You may consider doing that in every room, plus in the corners of the bed and crib (out of choking hazard range.)
As far as not buying the house, there is always a reason to be afraid: radon, asbestos, mice, spiders, mold, etc. Just take measures to insure the safety of your family and enjoy the new home!
By the way, I'm terrified of spiders and was bitten by a BR when pregnant with my 5th. I posted all about it here: http://www.welltellme.com/discuss/index.php/topic,3729.msg190380.html#msg190380