Diamonds / Substitutes ? 💎

Okay so me and my SO are very soon to be engaged. I know this sounds a little too planned but we have been looking together for an engagement ring. We don't have a lot of money but agreed to look together as I am quite fussy and for a 'time being' ring, I still don't want him buying and wasting money on something that's not going to last. 
Basically our budget is around $250 and all the diamond engagement rings for that price are super small or not good quality or grading. I just don't want him wasting his money on something that's not my style just because it's a REAL diamond. 
Basically I just want to know do any of you ladies have/had a simulated diamond or CZ (cubic zirconia) stone in your engagement ring. 
Please be kind ladies as we are hoping to save in the future to get a more expensive engagement ring but for the time being Im really considering getting a substitute to diamonds that's affordable, good quality and of course pretty hehe. 
Any shops / sites or pictures would be awesome ! ️Xx