How long would you wait for a proposal?

So I should probably say first off that my boyfriend and I did everything kinda backwards. Lol we have been dating for 5 years now and we have two kids together. Ages 3 and 4 months. We have talked about it and he has said many times that he wants to marry me and that he wants to spend his life with me but still year after year I still don't have a proposal. I have asked him before and he said it's more about the money it's going to take to buy a ring and plan a wedding. So should I just leave It at that and wait until we are more financially stable or??? Obviously I am not going to try and force him to ask me I'm just not sure on how much longer I should wait?