What engine? The SST was by FAR the most common model of Javelin, so there's not as much inherent value in the trim level alone. The Javelin was available with an inline six, or one of three V8 engines, a 290, a 343, or a 390. IIRC the 390 only showed up in "AMX"-badged cars, not the SST, making the 343 the hottest engine in the SST for '69. There were two versions of the 290, a 9:1 compression engine with a 2bbl carb and 200 hp (SAE Gross) and a 10:1 engine with a 4bbl carb and 225 hp (SAE Gross). The hotter of the 290 V8 engines was available only with a 4-speed manual using a console mounted shift lever. The badder 290 was supposedly underrated.
If it has the 390, it's rare. Incredibly so. If it's the 343, or even the hotter of 290, and clean, it's worth more than the rent if you don't mind waiting for the time it may take to sell. The lesser 290 will be more common and harder to sell, and it's arguable whether it's worth $8,500; you can probably get a little more for one, but it will take longer. If it's the inline 6, it ain't worth it.
ZV