If you can afford a DJ, personally I would go for it. For me, a DJ or band were one of my must haves for the evening.
My H2B is putting together a playlist for during the meal and in between band sets/end of the night, but the thing to bear in mind is that when you have a DJ, they can completely change the vibe of the room. They can see if people are dancing, and play the songs to get people up, slow it down when needed, as well as take requests and such. You also get the mixing / fade in/out with a DJ rather than that pause between songs where everyone does the awkward 'do we go and sit back down' shuffle.
If anything goes wrong with the playlist, you don't want your H2B spending ages tinkering with it trying to get i working again. And as you said, you don't want people trying to skip songs or cutting them off halfway through - I'd say if you do go down the playlist route, put the phone or laptop somewhere where people can't tamper!
My H2B is very frugal too, and I totally get the whole thing of not wanting to beggar yourselves for one day, but I genuinely feel that some sort of live music helps create a great atmosphere.
Also, re your comment on the photographer I would just say that the rings and the photos are all you have after the day is gone. If you don't want to splurge on a whole day photographer, (I get it, it's really expensive!) at least get one for the ceremony and group/couple shots afterwards, so you have some memories.
I hope this helps! X