you can get decent aftermarket upper wishbones complete with all bushes and upper ball joint.
Q and H, Quint and Hazel do them at most Auto factors, for about £40 a side i think.
however, the last time i ordered some, they gave me the choice of QnH or somebody elses, i asked to see one of each, and there absoloutley no difference whatsover, so i took the so called budget versions for £20 a side instead.
longevity really isnt an issue in my mind, how can it be, most Genuine Alfa wishbones are lucky to do 40/50k without tiring, creaking. and knocking anyway, so how much worse can aftermarket parts be?
the last car i bought, my sportwagon, had the uppers done at just 35k by alfa, and the lowers were replaced at 55k by alfa, but guess what, its now done 82k and ive just done the whole front end again dues to noises creaping in again.
save your money, just get half right complete units from a reputed motor factors, i use sutton auto factors of nottingham, and if something only lasted five minutes they'd replace it for me anyway.
as for poly bushes, i appreciate what they are capable of improving, but a lot find them a tad too hard and harsh, and transfer a lot of road noise too depending on the thier use.
as for doing them, well the top wishbones aren't too bad, there is an excellent how too thread somewhere which is pretty much **** on.
just check before ordering that you don't need other things aswell, such as ARB "D" bushes and drop links, as you might aswell do them at the same time for the price of them (£30 for pair of D bushes, £25 a pair of drop links)