First off, breeding a mojo to a bel will not produce all Bel's I have read the thread and want to make sure you understand that...... you will not produce any normals but you will have some single gene butter/lesser animals......

With 500 bucks at your disposal breeding to a bel wanting to make something cool.... I would honestly look into a sub adult Bumble Bee... Bees have come down in price significantly and there are some female Bees out there with some size to them at really reasonable prices..... I know this isnt the most powerful animal to breed to your bel but on your budget it is a 2 gene female and you will have a grab bag of impressive animals come from that breeding, also another benifit of a bee female is female spider gene animals seem to eat like pigs (atleast all of mine do) and grow quick...

you will produce
butter/lessers 25%
butter/lesser pastels 25%
butter/lesser spiders 25%
butter/lesser bees 25%