In my experience, to a jet operator anything less than turbine time on a commercial aircraft in a two crew environment is considered as 'low hours'. I believe the term to be not necessarily as it is written, I think it is more about experience than hours......when I got my first jet job I had 950TT, of which 700hrs was single crew multi-engine IFR on piston twins up to C404 size. I was still considered 'low hours' and had to do exactly the same as the 200hr cadets that I started alongside.
However, to a turbo-prop airline I would broadly agree with Scroggs that 500hrs is the sort of time that starts to make you just look that little bit more experienced.
I would say that after qualifying with your circa 200hrs the next 300hrs make little difference to an airline, but they are some of the hardest to get your hands on! As I mentioned in the first paragraph, extend this up to the 1000hr mark for jet operators. After 1000hrs it comes down to the quality rather than the quantity, so you need to be 'progressing' if you want to work for an airline. 3000hrs of instructing is really not doing you any favours if you want to be considered serious about an airline job (ok if the market has slumped and it keeps you flying). Having said that I always recommend the FI rating if you don't get picked up straight away after qualifying. Just look at poor Startbahn who has only added 90hrs in the last four years. He is still at the bottom of the pile with others joining daily, and others climbing rungs on the ladder and leaving him behind. I know it can be a bitter financial pill, but if those four years had been spent instructing and then possibly flying some twins I think he could well have had a job with an airline by now......
As ever, good luck.
PP