Once again I have to plug Q-Manager (hammer and tong.com) - the free version will do everything you need for basic FX playback, and if you need more than 2 channels or cue-able fades, the limited version isn't that expensive.
Given the budget, an instant replay by 360 systems is quite a nice unit, particularly for this sort of thing... I won't mention which worldwide known childrens' act runs all their backing tracks off one.
Go up a grade to a redundant pair of SFX computers, MIDI triggered so both play simultaneously.
And the final step would be something like a redundant pair of Pyramix, capable of running Olympic ceremonies and not skipping a beat or from memory, dropping back to the secondary... All with redundant power, at least one of which is UPSfed...