That's what things like False Life and Greater Blink are for.
Ethergaunt has +2 racial CON and +6 AC (+4 NA, +4 racial DEX) over a wizard of equal stats. That's not a small difference.
Put a 14 or even a 16 on CON during point buy, as you don't need the very expensive (in points) 18 INT, and you've already closed the gap by a fair bit.
With the usual 32 others buy, an Ethergaunt could be rocking something like STR 12 DEX 20 CON 18 INT 28 WIS 14 CHA 10 straight out of the gate.
With the usual +4 INT headband, it's going to be rocking a 21+Spell level DC without sacrificing anything. That's kind of crazy, given the nearly zero effort it took to get that high of a DC.
Should average to 46 HP or so, while the usual CON 14 Wizard 12 would have about 55 HP. In about five levels, due it's higher CON it will break even or surpass the pure wizard, and go on from there.