Reasonable price for a Tube Screamer

[Flavaham]

(I posted this in another forum but it might have been misplaced.  sorry)

I'm looking for a Tube Screamer.  Prices are so varied that I really am not sure what I should buy.  I feel like the original TS9 is the way to go but what is a good price for one?  What do the mods on these pedals do specifically?  Should I buy a moded pedal? Any advice with this would be great.  Currently I play a RAT.  I'm thinking I need two distortion pedals though.  The preamp I'm getting only has a clean channel.  I'd like to have a nice crunch for rhythm/blues playing (probably achievable with the RAT) and a sweet tube driven lead tone (TS).

Thanks in advance for the advice!