With respect to buying a metal detector, I would always advise getting a 2nd hand metal detector to start with. There are some really good old metal detectors out there. As a beginner, I would go for one with good discrimination such as an old Tesoro or a Laser. These are old but classic machines and I still use mine on particularly trashy ground or on productive fields with finds I know are close to the surface. You can get one for under £200. A more recent detector that has a little more depth is the XP PowerMax. Again, production has stopped on these machines but you can pick them up on Ebay for £200-£300.
If you want to go for something more modern, then I would recommend the XP Deus, which retail new at about £750.