I would suggest looking at Lightsail, if your credits stretch that far. The included 1TB+ of bandwidth is the reason for that. Bridges would typically see much more bursty traffic compared to relays or (especially) exit nodes; this does mean that the burst CPU credits on Lightsail (or the t-series EC2 instances) would pair up nicely.

I'd also suggest running in as many AWS regions as you're able, so that there isn't a lovely block of bridges all in one region.