THere is a thread on here in the Durango section, couple of pages in, might be worth you having a read through it -
Linky
You don't need a low profile one so I'd say you'd be fine with a 1258 but it's a little over your fifty quid budget.
This (
Clicky ) is brand new, RC Lazy are selling some stock off cheaper on ebay and it could suit your needs perfectly, super cheap too. But don't expect the quality of the Savox.
JE Spares have loads listed
Blue Bird 660 Metal Geared Servo (
clicky ) which is under £40.
This Futaba one is good and cheaper than the Savox as well as being a well known brand (
Click me )
Hi Tec are very good but not so widely used ? I don't know what that is, JE sell them too.
Or if you shop around you can find a Spektrum 6040 which is the same as the Savox 1258 but marginally cheaper.
You could always put a wanted ad on here and see if you can get one 2nd hand. Hope that helps.
Personally I'd go for a well known / used brand, Savox, Futaba, Ace / AE or Hi Tec are the ones I would recommend.