Depend on what HU being used to power it...... If using Pioneer DEH-80PRS or Alpine CDA-117E think should be ok.... Anyway, Amp can always be added on subsequent when you feel the HU lack "something"
If you get the 500 buck speaker now, and when you wanna add amp later, you will be restricted by it. If you sell it, you lose money and to use it with a good amp then it's the restriction of what you miss if you gotten the 1k speaker instead.
Anyway, it's your ears and money. Don't let the shop dictate what you want to buy. Also plan a bit for the future.
If you decide to stick to HU powering the speaker all the way, there are actually speaker specially made for this purpose that are high in efficiency so do not require amplification. For your information, this type of speaker also not cheap.... Maybe also in the 1k price-range....

Sorry to disappoint you, but there is difference between efficient and sensitive. Sensitive normally mean the speaker are easier to drive at nominal power. You still need some level of power and think both the Focal and Hertz are rated above 50watt nominal. As I think most HU have nominal of 10W to 25Watt and normally peak power between 40W To 60Watt, this case even at peak power for the HU would not be at the said speaker nominal power.
You need efficient speaker that can be played at nominal power of the HU. Something that operate say at 20Watt Nominal with Peak say at 80Watt. If possible sensitive as well of above 90db. In fact your current speaker are something like this. I am not sure what is available in the market as most of us will take the amp + speaker route as easier and in fact cheaper. I believe to get a good set of such Component/saparate speaker will not be cheap or else you see lots of them in the market. The only type I know is those high end co-axial speaker but maybe this would not be your choice also.
As such, what I can suggest is to look for a set of speaker with the lowest nominal power that you can find at your budget. It's not an easy task but I did manage to get a set of Alpine component with 40Watt nominal a few years back for use as rear fill powered by HU. Of course, it's rear fill only and my front stage have always been amp powered. Subsequent to that even the alpine get it's own amp and the HU then only as source without being used to power any speakers.
Curious if you want to power using HU all the way or maybe you be getting amp later? If getting amp later, then think carefully.