Wow, the price has certainly climbed over the last 3 years!
Don't assume that Spaceoar would necessarily be useful to avoid colateral damage. It might in some circumstances and your oncologist should be able to give you an assessment of whether that means you, or not.
With a G9 score I was prepared to pay for the insert but my oncologist suggested it wasn't necessary. This turned out to be correct. Despite being zapped with 81gy over 45 sessions I have had no side issues of any sort in the two years since my RT finished.
These inserts can have issues too, like shifting their position, so while we're all willing to do whatever it takes to get rid of cancer, there's a good chance a spacer might not be useful for you. I've seen it suggested that as RT gets more accurate and hence less likely to cause rectal damage, the need for a spacer goes down. Where it once looked as though spacers would become a standard procedure, their use seems to be on the decline now.
Jules