The savings are in RAM costs due to ELK stack basically not running under 4GB. And larger logs with stack trace are much slower compared to Loki. There's a reason there is no cheap ELK services.
Really depends on the size of each log and the complexity of the tokenizers. With 1 core you have time budget of less than a millisecond per log statement for processing and that doesn't include the relevant ES/Lucene operational overheads.
This is extremely doable for some workloads, but not others. Really depends on what you're stuffing in.
On a 1core 2gb vps it can do around 1200 logs/sec.
Compared to ELK, we're saving several hundred $ per month.