Here is what I have found to be the most economical front "bigger brake" upgrade for the 1st Gen RAV4. Going this route you will not need to get bigger wheels and aside from grinding the caliper bracket and using a 10mm wheels spacer it is a pretty straight forward upgrade.
Part you will need are:
1999 Celica ST Front Caliper Brackets
1999 Celica ST Front Calipers
1999 Celica ST Front Pads or OEM 1st Gen RAV4 Pads (they are the same) Shaved down to 15.5mm
2003 RX300 Front Rotors
10mm Wheels Spacer