Whatever you end up spending I'll bet you won't think it was a bargain. Good quality canvas work is expensive. It's also a great investment that will add to your enjoyment.
i got a quote for my Sundancer 250 which should be similar amount of material at about $3000 but it wasn't sunbrella. it was a verbal at a boat show so not an exact quote
I would guess around here in MN about $3-4K. The cockpit cover for my 250 Sundancer was almost a $1000. But the end result was much better than the factory SeaRay cover.