Get Guitar pedal or amp?

I currently play keyboards and whilst practicing I use a yamaha stagepas pa and amp. I am soon going a pick up guitars again and I am wondering on the distortion front of I am better buying pedals or buying a new amp for the distortion. I don't have too much to spend so it would be great if I could keep using my current amp, as it's a great amp. Also, what would you recommend from either. My main interest in music is power metal so thats the sort of thing I would eventually like to end up playing so I need distortion of that caliber. Thank you