if its a mk4 (96 on) courier it is dead easy to change. on the bulkhead under the bonnet. 2 hoses in (from front of bulkhead) 2 hoses out (back of bulkhead) and 1 electrical connector.
obviously wait till its cold to change it and top up the coolant.
valve only available from ford main dealer. no point from scrappys, very common fault, scrappy part likely to be as bad.
last one i bought was about 30 quid trade from ford
dave