Goretex shoes are pointless, whether for training or racing – the ankles are too low, they’ll soon fill up with water and then the membrane will hold it in, result = blisters. Anyway, all depends on your budget and whether you’ll keep using them afterwards, or will want to get rid, also – how muddy?
More expensive/popular shoes like Inov8, Salomon, etc, will find a ready second-hand market through the FRA’s forum Sales & Wants if you only want them for a short while/don’t intend to keep up the running. Salomon Crossmax, Inov8 Roclite, La Sportiva Raptor all worthy of consideration in this bracket, or for really muddy conditions Fellcross, X-Talon/Mudclaw, Crosslite from the 3 manufacturers respectively.
Less expensive but still re-sellable would be things like the More Mile Cheviots, which tend to get very good reviews on the FRA forum.