Prices kind of scale with how many rolls it would take to get an item that good. You could probably find one for 1 alch with a damage roll, a sick level 48 3-4 damage rolls would not cost 1 alch though, more like 4+ or 1 chaos + alch at least. Buying an item from vendor then alching it is a very cheap upgrade considering what you are using. I'd prefer to gamble 1 alch than buy something as good as what I 'probably' would have rolled anyway.
I just tried to buy a level 31 coral ring (bloody needed that ring for my treasure finder it had +18% rarirty and like +120 life and was jsut sick + damage +10% all resistance) for 2 alchs and a stack of chroms (lol)
'Someone offered exalted'
'Blessed and two alchs + stack chrom + 2 fusing'
'exalted is worth about 18 alchs'
'Oh ok then
'
People don't tend to want alchs for good items
I just got kicked again.. and I bet that rare amulet I just found will be gone.