Replacing transmission/vehicle speed sensor

Hey, 

This is my first post so please excuse my lack of knowledge. I own a 1.8T and recently it has been causing a lot of trouble, I took it to the mechanic earlier this year and replaced a bunch of stuff that ended up being really expensive. This week my car started going to third gear (I've got the 4 speed auto) randomly and staying there unless I manually select another gear. I performed a scan and the transmission gave me the fault code

"00281 - Vehicle speed sensor (G68) no signal- intermittent".

I took it to my mechanic and he said we had to replace the sensor and that it would cost around 200$ (I live in colombia so it was around 500,000 pesos). I currently cant afford that so i researched a bit and found out that ebay sells a sensor that fits my car for around 20 pounds with shipping (http://www.ebay.com/itm/SKODA-FABIA-OCTAVIA-SUPERB-SEAT-ALHAMBRA-LEON-IBIZA-TOLEDO-CRANKSHAFT-SENSOR-/321406842852?pt=LH_DefaultDomain_3&hash=item4ad55737e4&vxp=mtr).

I have never done a repair myself but Im willing to learn (plus i study mechanical engineering so its pretty stupid to have to pay someone to fix my own car). But before I go on I need to know if this is the part im looking for and how do I replace it.  Some time ago I had gotten the code 00529 -  Engine Speed Signal Missing so im unsure if this is the same sensor or if that's a separate problem.

Thanks in advance.