The Hornby model of the Advanced Passenger Train, strictly speaking an APT-P, was launched in 1980. Designed in conjunction with British Rail, it unfortunately enjoyed a rather more reliable tilt system than the real train. The demise of the prototype 5 years after the model launched led to a limited sales life with the final batch being produced in 1984.
Despite this, the model has always been popular on the second hand market. If you want a set, then many sellers on eBay will be able to furnish you with one for less then a price of a modern RTR big diesel.
What you get is a rather basic model. Admittedly the APT wasn't bristling with surface detail but current day modellers will I suspect be unimpressed by what is a very 80s Hornby production. Had the plan to produce a quick re-run a few years ago come to fruition, I suspect the forums would have been full of frothing demanding a few (read: complete redesign but sold at 80s prices) changes to the moldings.
With the immanent arrival of Rapido's APT-E, I'm sure we'll see the two models together and I have a feeling that the 35 year gap between them will be very obvious. However, with a Blue Pullman costing over £500, how much would people be willing to pay for an APT to more modern standards?