I agree (of course!) that the thing about the photography is that it is something that will last, forever, whereas the songs that are played will fade from memory possibly before the evening is over.
That being said, doing your own music is perhaps trickier than you might think. A good DJ, as well as having the right equipment, will "read" the mood of the event and the moment and play the right songs at the right time - up tempo, fun songs when people want to dance, a bit more gentle when people want a break, etc.
Given a limited budget, as most of us have, as the other photographer on the thread said, I would cut back on favours, gifts, gimmicks, etc. to allow you to have both photography and a DJ. Renting that illuminated "LOVE" sign will make no difference at all whatsoever to the extent to which you enjoy the day, your guests enjoy the day, or the memories of the day in years to come. If you've cut back on those things and you still are hitting a budget limit, consider cutting back on alcohol, the cake, the cost of bridesmaids dresses, etc. all of which I personally feel also make less difference than most people realise.
And don't get me started on fireworks...
Hope that helps!