I paid 100.00 for a normal red tail boa from a local breeder here in Phoenix. I paid 150.00 for a hi orange colored redtail from a breeder in Texas. A decent boa bred by a small reputable breeder will range between 100 and 200 and higher for unique colors.
My new boy Crush whom is 1 year old is worth every penny of the 150.00 I paid for him. I personally would steer clear of Petco.
IBD disease could be present as well as other issues, mites etc. Just my personal opinion.