wifi problem iphone ios 7

so hey everyone! recently i have encounter a problem with my wifi. it previously runs on ios 6.0.1 and the problem is that the phone could not locate any wifi signal eventhough i am near the router. Switch off and on the router, reset network settings, airplane mode and reset the network settings, all to no avail. i've even update it to ios 7 and still same problems occur. Sometimes my home wifi appears but then it took awhile to connect and soon after,BOOM disconnected. I also have tried to forget the network. So anybody could HELP ME! if it is internal hardware stuff, could u tell me if it is cheap to repair it?