i have a trek 4300 disc. upgrades: xtr r derailluer, xt cassette, sram 9spd chain, bontrager race lite stem and bar, lx shifters, hope mini rear disc brake, and one lx lever for the stock front disc (mech). I'm debating getting a used p.3. how much do you think they will go for. or a new fork for around $300-400. What do you think i should do and why?