Resolve Wi-Fi Connectivity Issues

I have a stubborn Wi-Fi / internet connection problem that I can’t pin down. As a recent Computer Network Technology graduate I’m comfortable with TCP/IP, routing, switching fundamentals and basic troubleshooting, but this particular issue has out-lasted my usual fixes... (Budget: £250 - £750 GBP, Jobs: Cisco, Linux, Network Administration, Network Monitoring, Network Security, Troubleshooting, WiFi, Wireless)