Hi I would like to know how much would you pay (or have paid) for installing gears? and how much for reconfiguring a speedometer?

Depending on who does the install, it should vary between $150-$325 for labor.  As far as the speedo, what year is your car? The earlier cars only require a different speedo gear install in the trans., which is about $20.  A '99 up 'Stang will require someone to recalibrate it electronically, which should cost around $200-$300.

d'ouch fo the recalibration cost!

I have a 2001 Gt 5 speed i've already paid 180 for gear installation (4.10 btw), I will pick it up this evening! but refused to pay 100 for a box that would fix the speedo issue, because when i bought my set at summit someone told me, better take it to my local ford dealer for that, but wanted to ask you first

But i will see if i can live with my speedo off (in certain way)

even if it will cost a $100, it is still relatively cheap compared to the depreciation of your 'Stang the extra miles on your odometer will cause. Just though I'd mention.   

Right!!! I never thought of that, Thanks for the tip