>>>Rioja is graded in 5 categories
Who by?
Rioja is classified as follows:
Rioja (less than a year in oak barrels)
Rioja Crianza (at least one year in oak, and at least two years aging in total)
Rioja Reserva (at least one year in oak, and at least three years aging in total)
Rioja Gran Reserva (at least two years in oak, with a further three years in the bottle)
Unsurprisingly, those wines with the greatest aging tend to be the most expensive. I'd expect a 2004 or 2005 Rioja to be pricey (particularly if it's well-oaked) but I'm a little surprised that a 2006 vintage should attract a fairly high price:
http://www.decanter.com/wine-learning/vintage-guides/regions/Spain-Rioja
Your post makes no reference to the oaking of the wines (which adds to the cost). Further. 'Tempranillo Rioja' is meaningless (or, at least, tautology) since Tempranillo is the principal (or sole) grape in all Riojas.