500ml is probably too small (my starter size is usually about 750ml-1000ml), but you could make use of it with a smaller starter if you either use Fermcap and/or boil the starter in another pot before transfer to the flask (and, again you may need Fermcap during the ferment to prevent a mess).
In my opinion, even a small starter is better than no starter at all.
Edit: just re-read that you said "beaker" not "flask". Probably not worth it at all with a beaker that size - better to use an old growler or half gallon mason jar.
Atomic Dog Brewery
On Deck: Centennial IPA, Dry Irish Stout
P: Cascade Pale Ale
T: Carbed Crystal Light, Root Beer, Vanilla Cream Soda, Tripel IPA, Apfelwein
e^(pi*i) + 1 = 0