"Morphs" of ball's and boas are still quite expensive compaired to morphs of like corns and kings as others have stated.
Balls I assume it is because of the small clutch size so it takes longer to build up stocks of morphs in the hobbiest trade.
Boas I don't get, they through big clutches and breed really easy. I figure the market has to come down at some point. It happened with burms and retics it will happen with boas and balls too. Both have come down a lot already as Judy stated.
If I were you I would either
1. Stay on budget and look at normals but have fun look at LOTS of them, look for something that you like. Unique shades, patterns etc are on every snake just look for one you like. I have seen some BEAUTIFUL normal balls with cool markings. I don't own any yet but I have almost bought a few and it was always "normals" I have found the most beautiful.
On boas the same is true, there is nothing much more beautiful that a nice normal red tail, they are simply stunning.
2. If you want something unique like others suggested you can look to the colubrids. Amel Kings and Milks are really coo. Lavender corns are beautiful and they were well over 200 bucks a few years back you could now buy a pair under 100.
Just don't over look normals, to me the species and what it offers is always more important then the vanity of a morph. How many people have all types of morph corns and they are just jaw dropped by a "normal" Okeetee or Miami Corn? Both of which you can pick up at shows for say 20-35 bucks.
Same with boas! Look at a 6-7 foot adult Redtail and you just have to pause and think about how amazing nature is.