Our contractors' combined charges for mowing, turning, rowing up, baling, wrapping come in at about £8.50 a big round bale, plus they fill up their tractors from our diesel tank as they leave. (And they use a lot of big, thirsty machines.)
We also then have to pay them by the hour, plus fuel, to lead the bales in for storage, as we don't have the squeezy arms.
Fertiliser is around £400/T? And you'd have to pay someone to spread it too?
Silage bales sell for £18-£26 each around here, if they sell at all - there isn't always a market for them.
If you can be sure of hay weather, you spend a little more on turning (you'd turn one or two more times, at least) but save £3-£3.50 per bale on wrapping, plus if you have a tractor and back spike, or loader and gripe, you can move the hay bales around yourself.
Large round hay bales fetch £15-£25 each, sometimes up to £30 when forage is scarce, especially if it's good hay. You can always sell good hay. But you do need somewhere under cover to store it until you do sell it.
You need contractors who are willing to fit you in when you need to be fitted in, whether you make hay or silage. But there is more leeway in when they do all the various operations for silage than there is for hay - it's no good baling hay in the late afternoon/early evening as the dew is getting onto it, for instance.
If your weather is iffy, and/or there are only a few short windows of opportunity to make hay or silage (and everyone else will be wanting the contractors at the same time as you), then personally I'd take the £500 and the total lack of any kind of stress or uncertainty, and thank your lucky stars!
But on the face of it, yes you could potentially spend what, £1500-£1900 making 130 bales and sell them for an average of £20 apiece, thereby almost doubling your net income. (Except for the years when you got no crop at all - but hopefully that would be fairly rare.)