If your going down the 2nd route you would prob get a decent HT for €700-€1000 and maybe a little more for a full suss. There are bargins to be had these days in the 2nd hand market.
As far as selling it on.! If you have something half decent and the price is right you should be able to sell it on easy enough.
Check out epicmtb or madmtb, theres always someone selling something there. Or even adverts.ie and boards.ie
If your on a budget, hardtail is the way to go, you'll get a lighter bike and better spec for the money.
Some online retailers might still have good deals on new 2011 bikes in stock which you can get really good discounts.