So far this is what I have done with my 1/8th truggy

Second hand Hyper ST PRO Roller $200AUD
Motor: Tekno Neu 1515/2.5d - $220USD
Motor Mount: RCM - $40
ESC: MMM - $140
Batteries: Polyquest 6s1p 6000mah - $270USD
Servo: HiTec 7955TG - $120USD
Charger: Hyperion 0610i - $150
Powersupply: 24v 13A $100AUD, but got it free from work
Radio: Spektrum DX3S - $220USD
Total: About $1300USD

The vendors that I used or would recommend would be this sites shop (motor/esc/batteries/mounts etc), Towerhobbies.com (general parts/hop ups), Impaktrc.com (motors/pinions), searching Ebay for cheap rollers and misc parts, rclipos.com (charger/lipos), Hobbycity.com (cheaper lipos, Zippy brand). Have a look around these sites and the prices. This site (rc-monster) is an abundant source of information on all aspects of going fast and over the top.

Since I am in Australia I had to get a lot of things posted, which you may also have to do. So add another 5-15%.

Using a GPS so far I have clocked 45mph.

Of course you can choose cheaper components to get the price down, but for the speeds you are aiming for this may not be possible, without burning something up. As you can see the main cost of going fast are the batteries, motor, and ESC. So my advice would be to either rethink your budget, or your goals.

Going to a larger scale will also cost more.