Yeah its common in bikes, and cars, and lots of other things, that the parts cost more than the whole. Think of it as a kind of bulk discount.
As for your tyres, how are you splitting them?? Scraping on rocks? Squashing the tyre on a kerb/root/rock by ramming the object too hard? It would do you well to seek out some double or triple ply sidewalls. They have, as the name suggests, 2 or 3 layers of rubber in the sidewall, rather than just one, and so have better protection about both kinds of damage I mentioned above. They also allow for lower pressures, and as such are often marketed as DH or downhill tyres.
I don't think getting a new wheel will solve the problem, its likely either your choice of tyre or your style of riding thats doing the damage. And if you are looking at bikes for the same price as a new wheel, you need to look higher up the bike food chain if you want anything decent.
You haven't said what tyres you use, but you could look into Maxxis Highroller DH tyres, which are nice and sturdy, and set you back about £20 each, or you'll find online deals for 2 for £30. I used to use them, and they are great tyres. Heavy, but then they have to be if they have a thicker sidewall.
Whoever said folding kevlar tyres are stronger - I never heard that before. A folding tyre's only advantage is... it folds. And they're lighter due to the nature of a folding bead. Your bead could be made of diamond and it would not have any effect on the strength of the tyre.