"is there another way ecept to use an expensive vga to video convertor? "
That kramer rack is worth several macpros !!! not so easy to setup, if rented. And has only one pgm output... so no real multiprojection.
Use a vga box on each output ! 80 $/€ for a "working" one.
Of course, all that depends on what your performance is, so you might want to throw in some details, if you want people to give some useful advice !
How many screens do you have ?
Do you need a different image on each screen ? (in which case you don't need several graphics cards, but a 1x8 VGA distributor)
What sort of mixer are you planning to use ?
Do you NEED to mix analog video ?