Video: How to Stretch Carpet
Carpet with pad purchase cost $10-20 for really economy cheap stuff, $20-30 for normal brands, and $30-50/SY (square yard) for high-end carpet, to $100 or more for custom or gold thread and such.
Installation cost does not change much depending on what varpet is installed - generally about $10-20/SY.
So, for normal medium-range carpet I would assume $30-50/SY.
1 Square yard = 9 Square feet