Many moons ago, I build myself a temporary T5 39W * 6 unit. Was fun doing it, but after a Saturday putting it all together, cutting and stripping wires. Trying to get those wires into the bloody ballast. It left me wondering if I really saved any money?
The 3 ballast units cost under R200 for 54W. The end caps is about R15 for the normal non-waterproof type (if I remember correctly) 15 * 2 * 6 another R180.
So I'm already at about R800 for just the ballasts and en caps, never mind the reflectors, splash shield or something to screw all of this onto.
After the new globes etc, my unit DIY worked out the same as a new T5 39W with 6 new globes included. Given, they were not the best quality globes, but were OK for at least 3 months. Would have been better for me then to rather buy the new unit. Never mind the for sale section. So still my advice, get the prices of everything, check the for sale section, and compare the prices and effort.