Sakura is currently on sale on Hobbyking for 55 EUR in the EU warehouse. That leaves the BT-4 looking pretty expensive :-)
Regarding the parts cost - I usually broke the same part on one side multiple times on the same corner of the track. And here the Xray parts cost cca the same for the one part vs 2 Sakura parts. So for me the cost of Xray was roughly the same.
The one thing that the BT-4 looks to have much better is the top deck. No obvious weak spots like on the XI Sport. I broke 3 or 4 for of those, all on the same spot just behind the front screws.