myprospace.com is a pretty straightforward name; says something obvious, but a little clumsy in the telling and I wouldn't value too high.
If I was appraising it without knowing you had an offer, I think I'd say:
reseller = hi xx, to low xxx because it has some obvious meaning and value, but not juicy or exciting
end user = if motivated, still no more than low xxx.
If you have an offer for 300, personally I'd settle for that in a second. But you may want to feel out the buyer. Hard call; sometimes the first offer they make is the absolute ceiling, they put their top offer forward and won't pay a dime more - and sometimes they're putting a test offer forward as a feeler and are actually prepared to pay much more.
In this case, if you REALLY want to squeeze a little more out of that orange, I'd squeeze carefully and only for another 50 or 100 tops.
But, you could prove me wrong. Only you can read the negotiations as they unfold.