You really don't have a choice if you want it fixed. I would go ahead and pay to ship it back...but I would let the builder know how much shipping was. If it is a stand up guy and the problem was his fault then he will refund your shipping expenses. If he is not willing to pay for your shipping, then you still need to have your rifle fixed so if you want it done you will have to pay shipping. hopefully he will fix it without any more trouble than that.
I sent in my 14 year old Glock 36 and was out ~$60 in shipping to them...they covered return shipping and completely rebuilt it for no additional charge...even replaced 4 mags with brand new ones.
I sent in my brand new walther p22 using their shipping label and they covered return shipping as well...however I still will not buy another walther...not impressed with the quality of this gun even though it is working now.