right now it's 100K Avios so that's a nice deal, if you can spend the 20K in one year... Though 50K off the bat.
If you can spend 20K in a year... then you should aim for 30K.. which would get you the 2 for 1 voucher and put you at 145K miles... 2 for 1 is excellent for First.....
I can't seem to find any availability for LAX-MBJ from July to September though and am tired of searching for any... it's segment based travel though so I would imagine it would be priced like LAX-MIA + MIA-MBJ....
FDW