[tor-relays] A question about transfer - any advice?

I'm running a Tor relay and everything is going great so far, but since I'm hosting on a commercial VPS, I have limited transfer (1 TB per month, overage: $0.02/GB). As such, I've set accounting to 10 GB per day so I'll at most use 620 GB in any given month and don't have to pay any overage costs.

Q1: can I increase this limit without paying extra?

I'm seeing that this 10 GB is hit very quickly, today within 9 hours.

Q2: how can I adjust the bandwidth limit (80 Mb/s, burst 160 Mb/s) so that this 10 GB is more spread out over the day? Would it help to make this, say, 20 or 40 Mb/s?

Thanks!

Ps: if I haven't supplied sufficient details, please feel free to ask