When you decide to get another ball python... ;)
You should base your decision on your breeding goals and general idea of which direction you want your collection to go in.
Your best outcomes for the some of the single gene animals in your price range would be:
Pastel x Cinny = Pewter
Pastel x Mojave = Pastave
Pastel x Spider = Bumble Bee
Pastel x Pinstripe = Lemon Blast
Pastel x Fire = Firefly
Some Second generation projects could lead you to (best results):
Pewter x Cinny = Super Cinny, Silver Bullets, more Pewters
Mojave x Pastave = BEL's, Pastel BEL's, more Pastaves
Firefly x Fire = Super Fire (Black Eyed Lucy), Pastel Super Fires, more Fireflies
Just some examples and ideas for you, let the addiction begin.