Quick rough estimate on breakdown:

1/8e Buggy
HB Ve8 - $300
Tekin RX8 - $300
XP 1015 servo (.11 transit 201oz torque, more than enough) $100
Airtronics MX Sport 2.4Ghz radio $100

We are already at $800 and you have no batteries or charger
This is also a great point of debate. Do you go with the Hyperion/Maxamps/Reedy packs at $100-$250 EACH or the HobbyCity packs at $40-$60 each + shipping?
Then do we get the Hyperion Duo/Checkpoint/Venom Pro for $100-$300 or the Turnigy Accuel for $35 and a power supply for $15?

I run a Duo with the HK batteries and do just fine.

But either way you are at your $800 budget and are spending a minimum $200 more for batts/charger and all the way up to $700-$800 additional depending on how crazy you want to go.

Now of course you can buy used rollers, preowned brushless setups, etc. Or even find people selling JR 9100 servos on here NIB for $80-$100 and piece it together over time for less but its still very expensive.

For 1/5 you are looking about an additional $300+ just to get going. You need better servos, higher cell count batteries, conversion kits, etc. And I have never seen an indoor track that allows 1/5 scales and surely not to race! Imagine cornering those!

Good luck with whatever you choose though and have fun! 1/8e is a blast. Sadly I am selling mine.