Well first off believe it... whether you can afford it or not. People dont realize these fancy gadgets are very good when they work, but fixing them is a nightmare in itself. I've had issues with those rails in different imports and luckily I once just aligned them myself and never messed with the Sunroof till when it was time to sell the car. Unless you grease em frequently and care for them, they are bound to fail. Now I'd say 700 is a little too much. I was quoted 125 for a bimmer and labor to about 200. Sounds like yours are frozen. Just leave it alone and spend the 700 going to the tanning booth instead. I mean do you REALLY need to have sun-rays glow on your sholders and the loud wind messing your hair? Or is it the moon-roof? I admit that can be romantic when looking up a starry night, but you can just pull over and do that from the hood as they show in movies.
Either way, you keep that $700, swallow your pride and drive with it sealed. When I bought my Volvo it had no sunroof- you know what I said? Thank goodness!! Now if your sunroof is open then you have a different problem..but if its frozen shut, just live with it
good luck