What percentage of your weekly wage or net worth are you willing to kiss goodbye? That's the only metric that counts really. I started off with a couple of hundred quid and then went from there.
Are you looking for long term gains or do you want to get out rapidly with some profit?
Thats the perfect sense regarding investing your real job money or the money you have got in savings. Only contribute that much amount of money which is not required by you for your daily life needs, smooth running of your entertainment and most important having the xyz share in the savings of emergency cases.
For me, I started with couple of hundreds too and never dared to put more than that into trading. I got some good bucks eventually for keeping and holding for long terms. Then I mostly put money which I earn online. Thats a good deal too.