well if you get it for $250 that is a bargain. you say it runs, is complete, and original and has all the hard to get parts like original blinkers, lights and guages, well at
least a few $1000 i reckon maybe $1500-$4000 a little hard with no photo. and there could be someone out there who is willing to pay double that because they realy want one. These sort of 70's road bikes are worth much more than dirt bikes from what i have seen what people are willing to pay for those. i would never expect to buy a decent 70's road bike under $2000 usually for under that they are very tatty and weathered and abused, if i did get one i would think i got a lucky deal and they seller didnt know really what they were selling and didnt know what was the right price to ask. its a bit like my 250Z, i only payed $400 for it which was an extremly good deal even if you take out the rare factor and it was easily worth $1000 or more but the guy i bought it from didnt really know what it was and to him it was just an old suzuki bike for blasting around the farm and he was more of a modern dirt bike guy. And i also bought a 90% complete PE 400 for $50 which was just missing a pipe, correct rear fender/light, blinkers etc and head gasket, as the guy i bought it off had no idea of the value and only asked $50 for it so i bought it.
the way to get the best idea is to go down to your local newsagent and buy a copy of Just Bikes and Motorcycle trader and see what similar bikes are going for thats what i do. There has been a steady increase in value of the 70's jap road bikes lately eg T500's GT380's XS650's, RD's R2/R3 yams and the 2 stroke kawasakis as many people are re-visting their youth and restoring these bikes. Back 10 years ago eveyone just wanted 60's and 70's triumphs Nortons and BSA's they are still popular but now people are getting into the 70's jap roadies. I could make a living just on working on 650/750 Triumphs, thats how common and popular they are.
Also search on ebay and see what others are asking.
BTW you know this is a dirt bike forum