Wanted to add on that bounty size, at least from contacts, is also dependent on relationship with that particular contact. I generally don't see million credit bounties until I've gotten a contact up to about 8+.
As a new player, I'd also offer some guidance.
First, your fleet mix is off. You've got 2 salvage rigs which bring nothing to combat, but you've only got a buffalo to haul the loot they are generating. They are otherwise horrible ships logistically, as stated in their description -- they can't carry the supplies, fuel nor crew they require, so they need other ships in your fleet to carry that for them. Salvage rigs are more cruiser/capital fleet ships. You'd get nearly as much bonus salvage from running 2 shepherds in place of your second salvage rig. Shepherds by comparison would give you a sizable 100 cargo space per, and they'd haul 40 fuel per, giving you a pretty decent range for hunting down bounties. Swapping out your 2nd salvage rig; that's 200 extra cargo and 80 extra fuel, for the same fuel/ly cost, only 3 supply more a month in maintenance, and 10 extra crew (but hey, now you've got space for 60 more crew that your salvage rig didn't provide). Plus they can actually help in a fight. Early game, those borers can help your destroyers not get swarmed by frigates, as the enemy AI will waste time trying to avoid letting borers flank them and attack their engines. They also do decent point defense if they aren't overwhelmed. And the shepherd brings a universal slot and a ballistic slot; enough for a machine gun or vulcan to allow its own point defense, plus some swarmers to harass or take out heavier fighters.
While on the subject of salvage; you're probably not offsetting your costs when you think about it. Those 2 salvage rigs cost you $1000 a month in supplies & salaries, not to mention $120 in fuel for every lightyear in hyperspace you're traveling, plus the indirect cost of tying up your buffalo and other ships' fuel storage and cargo storage to support the salvage rigs' needs that they can't carry themselves. Your post-battle scrap from your average $50k bounty you're hoping to get is what; 50 supplies? So with a 44% salvage bonus from your 2 salvage rigs, giving 20% of their bonus on post-battle salvage, this would yield you an extra 4.5 supplies. So $450 of extra loot, maybe $600-800 when you add the bonus fuel, metals, and heavy machinery. If you've traveled more than a light year to that battle, you've already lost money.
Downgrade to 2 shepherds, and you can assign them to escort each of your destroyers.