The Bitter Well
As per the D20 SRD, Prestige Classes don’t count for the purposes of determining if a multiclass XP cost applies.
As per Unearthed Arcana p.18, ECL due to race can be bought off.
I will be using the Natural Waste Hazards rules from Sandstorm, p.12 Athas’ day time temperature varies from Hot to Extreme Heat during the day and can get as cold as Cold at night. This is why many travellers seek shelter during the day and travel at dusk and night.