The videoblaster uses the 1248, other components you mention are not cheap either.
So there goes your 50 budget.
You seem keen to experiment so do not let me put you off.
NardJ:
. I am wondering if there are refresh rates far below 60Hz... have searched, cannot find them.
There are but the display rapidly becomes objectionable (flickering), monitor would have to be adjusted also.
EDIT
You might also consider the effect on a person with epilepsy also
PAL uses a 50 HZ signal but the generation of colour is more complex, it is possible to get a usable monochrome signal though.