I LENT my money to my LG to arrange the wedding..His incoming all contributed to his family at that time, he has no money for everything. but we have to marry then, so i lent him some money to buy the Ring and arrange the wedding. It was so sweet, although not big. 0.38 . He proposed in a beautifull hotel garden, really sweet.
Now His finance is more than enough for everything. So girls shouldnt focus on the money in a short time, but value the meaning of love.
my suggestions, give some hints to you GF, or ask her good friends for the idea. A general rule is The diamonds price shouldnt be less than 1 month of your salary, but if your salary is more than 8k, consider carefully.