Cydia costs $9.99 on iPod touch.
Mostly it costs $200, but at target it costs $190, And on amazon it costs $189
You can't actually 'upgrade' and old ipod touch to a 4th gen. You could sell your old ipod and use the money plus some extra to buy a 4th gen.
The iPod Touch 8gb costs 199$
about £90
350000
$600
$50.00
$259.99
nothing
199.99
About $180.