Op, perhaps you could explain this to me because i have never been able to understand it. You've only been with this girl 6 months yet you want to rush into marriage? Your finances are struggling, yet you want to get in even more debt to buy a ring? (Not to mention the cost of getting married!)
If she is the one you're going to spend the rest of your life with...what's the rush? Give yourself something to look forward to! Why cripple yourselves financially for no gain, when you could propose to her in say 3/5 + years time? Also, rather than doing it now with a cheap ring, getting down on one knee at mcdonalds, if you wait a few years you could use the ring you really want and do it at a truly memorable, romantic location such as on holiday somewhere.
"Never make someone your priority, when to them you are only an option"