There are Vector monitors for old arcade systems, which are better than both scopes and the vectrex, but sadly these are not at all cheap.
Scopes can get quite cheap/free (old analog scopes are often considered ‘junk’ rather than ‘vintage’) if you live near the right kind of e-waste dumpsters or know the right people, but once you get shipping into the equation the prices tend to increase.
If i recall correctly the vintage arcade community have figured out how to convert old b/w CRTs to vector ones by replacing most of the drive circuitry and i think there might be kits, but this very quickly turns into the DIY high voltage domain. (aka. the “this will kill you if you mess up” category)
Something like LZX cyclops or some other way to get at an ILDA laser would also qualify, but again leaving the price category you were thinking of. (Diy is again a thing here, but please don’t blind yourself or the audience)
Someone else can hopefully fill in some software alternatives