Dual Power Supply Build with Buck Converter
Considering +-25V and 5A imply 250W, the option to design your own inverting supply are relatively slim – inverters put an especially high demand on both the switch and the inductivity, so this might be hard to achieve without killing your budget.

So, the next approach would probably be generating a ground +- ~30V with a transformer with a middle tap on the secondary side. Then, for the +25V, normal buck controller, and for the -25V, negative output buck:

I'd have to admit that I've never done a negative output buck  with significant currents – however, here's an application node from Vishay explaining the principle behind that idea. Note that this might or might not work with every Buck controller out there – you should ask in the manufacturer forums if you want to build this with a different controller IC.