I recently happened upon this bike in my local CL and am considering purchasing it. I mostly bike for fun with my two sons on pavement and smooth trails, but occasionally commute 3-4 miles to the grocery store. Looking for your help in establishing a fair offer taking into consideration maintenance on these vintage parts. I used to have a bike similar to this one when I was a teenager and was immediately drawn to it.

Asking $225 o.b.o. Cool red vintage old school Mongoose ATB early mountain bike by B.M.X. Products, Inc. Based on the serial number (M5-.....) it is a 1985 model from back in the day when Mongoose only made high-quality bikes. Good survivor condition with mostly original parts. Triple butted 4130 chromoly mainframe and chromoly forks. Numerous braze-ons for touring. Original old school drilled 26" Pro Class wheels. SR MTS 100 double stem. MTB 100 bars. DiaCompe 980 cantilever brakes. Cool motorcycle-style brake levers. Old school bear trap style pedals. Cables and Rear derailleur have been replaced. Oury grips and Kenda tires are relatively new with less than 50 miles of riding on them. I replaced the original seat with a more comfortable Forte one, but still have the original seat if you want it. More info on Mongoose ATB available via www.vintagemongoose.com.

Original bike specs are available via http://www.vintagemongoose.com/pdfs/mongoose_cat85.pdf

I am also considering a few others, mainly a late model (exact year unknown) Trek 830 and a mid-90s Specialized HardRock.
I appreciate any advice you may have to offer. Thanks!