I would replace as an axle pair, unless nearly new and you are replacing one like for like. Avoid no-name and cheap brands you have never heard of, they don't last. Fit a known brand such as Kayaba (KYB), Sachs, Monroe, etc.
Can't help with dealer costs, I only use a garage for my MOTs, but rear shocks is a straightforward job that any competent garage should be able to do while you wait.