Invisalign for Bottom Teeth Only?

Invisalign just for bottom teeth is possible but not recommended. Teeth, both upper and lower should be in harmony with each other so they are stable and don't relapse and cause an imbalance. Since overcrowded teeth also affect the bite its important that you get the treatment for both upper and lower teeth.
Theres also no difference in the cost if you only get the lower teeth so may as well get both arches. The cost for Invisalign at our practice is $4000.
Hope this answers your question. All the best. 
Warm Regards.

We usually do not isolate treatment to one
arch only. The bite will change periodically throughout treatment and if both
the upper and lower aligners are not being worn, it is possible that the bite
will be affected in an adverse way.