If you can get $250+ for a Grand Prix I say go for it. Keep in mind, this is an Asian built Raleigh which are typically valued lower than a British Raleigh. Don't get me wrong, I love these Raleighs and they are great values for the buyer but not so much the seller. There is a top of the line Prestige on eBay right now that didn't get a nibble at $299 + $12 shipping. It's relisted as an auction and I bet it goes for $250. 3 notches up from a Grand Prix.
I posted an inquiry about a Schwinn Super Sport and got mostly values in the $200 range with high side of $300. Tenax tubed bike that is arguably superior to a 531 front triangle Grand Prix. I own an 85 Tempo and an 84 Competition and am confident in the comparison.
But as we know, it only takes that one person to prove any of us wrong! Try listing it at what you want and let us know how it goes.