In today’s age, there isn’t the cost savings we saw in the 80’s/90’s for custom rod building. What you can gain is having subtle to major improvements from reel seat placement, guide spacing, quality of components,…and so on. Before you start, you should always know what you want to end up with. If you know someone that can mentor you in rod building, there are a lot of “tricks of the trade” you can apply.
For start up, the cost isn’t too bad if you keep things simple. Then add specialty stuff as you find a need. Some of my most favorite rods are ones that I designed for very specific applications. I took a Sage RP-II 4wt flyrod blank and built an ultralight (8′) that has a significant backbone, yet I can pitch 1/32oz jig / mini-mite a country mile. Caught more 10# + steelhead on that rod than i can count
