Caver makes a very good point whereby the retailers apply a pressure of their own to urge people (well, men, let's be honest) to burn huge amounts of cash on something which is merely a visual recognition symbol of a question.
This is not an issue that is simple as that tho', as there are inferences of status involved for both sides of the proposal and the problem is further clouded by opinions that are external to the couple.
I know that the latter played a role in my ring choice. I know full well my missus would've been happy with a 'cheap' ring, it was the 'question', asked the right way in an appropriate setting, that she wanted. However, there was no way I was going to put a bottom-end ring on her finger.
Why?
Because I did not want people to look at the ring (as they inevitably do) and ponder to themselves "Is that all he thinks of her?". It's silly but it has an effect. I spent a quarter of a years income just so other people would not think that my love was not real. Also, I did not want my missus to be ashamed when people asked to see it, so I spent more on that diamond band than I have on all the cars I have ever owned combined.
How stupid is that?
EDIT: BrandiJo makes some very good points too. In fact, she also raises an intriguing cultural aspect with regard to wedding costs. It seems that in America the trend is for the costs to be shared by both families and for the 'price tag' to be quite low. In England, it is still held to be the bride's father's responsibility to foot the bill and that bill is an average of £18000 ($36000). I think that is wrong, plain and simple. Most families are not forging great political alliances with their betrothals and that magnitude of expenditure would be crippling for the majority of families in this country ... and yet they still do it!?