That one isn't mine, just the first picture I found on my phone, but they seem to go for about £350. There strangely isn't much difference in price between a good SE upgrade and an excellent one.How much do you think a pristine Gemini Integra board like yours goes for these days?
Truthfully there isn't really a going rate, it is just hit and miss how much the seller asks. There aren't enough of them about for a standard price.
My SE has the slightly older Total Systems Gemini Ultra on it at the moment because I was able to find a 50MHz variant.

