What To Do? =(

[Avensis_GLS_2001]

basically about my oil comsumption they cannot fix it under warranty as its ran out. they told me it will cost £11k to fit a engine or 1k for a new catalyst sensor! what should i do? the code was p0420 on the report it says cat below but 2 weeks ago toyota told me it will cost £380 to replace the p0420! what should i do? im lost also my MOT is next month! the oil thing after toyota put new oil in it hasn't burnt any oil at all! im lost! someone help me! its A 51 plate avensis 1.8 GLS model with 52k on the clock!

[cmia]

what kind of services has the car got ?

[Avensis_GLS_2001]

its only got up to 39k because of the previous owner lost the fsh booklet! how much is a po420 to get fixed normally? its a catalyst below something like that!