I never got a ring from XH, he didn't really propose as such, we just agreed to get married. I ended up choosing a cheap (£10 ish) silver ring from a market somewhere which I wore a few times, but it didn't really feel special enough to matter.
I got a plain platinum wedding band, which did end up pretty scuffed and dull after 14 years. The original £400 price tag, which was allegedly just the cost price per gram of platinum, gave me £170 when I sold it last year.
I always felt a bit sad that I wasn't worth buying diamonds for, he never bought me any other jewellery (I don't wear much anyway, just bracelets usually) and was a bit tight generally, so I should have taken it as a sign.
Is your fiance generous in other ways? If not, this is probably a sign of things to come for you.
FWIW, my current partner bought me an eternity ring (I'm technically still married to XH so although we've discussed marriage in our future, it's not an engagement ring!). DP asked me to point out some styles I liked, I was looking at white gold rings for around £200-300 and he told me I had undervalued myself and that he wanted to spend about £1500 on it. I was horrified! I couldn't bear the idea of spending that sort of money on some jewellery.
However, since buying it (he took store credit and pays monthly) it makes me feel happy and cherished every time I look at it. It also makes him happy to see it sparkling away as a symbol of his love for me for all to see. Sounds daft and soppy, but I finally see what the fuss is all about!
I'm sure I'd have been equally happy with a £200 ring if it looked the same and sparkled the same, I have no idea about diamonds, but it's the thought that counts and if your DF isn't pushing for you to have something to wear on your ring finger, I think it's a sad sign. If it's really the money then he needs to be having a conversation with you about budgets and compromising, not about carpets and gardening!