Pli55ken Depends on the ship and what you want to do with it.
If I want a trader I'd say you can get away with less than double the price
Example (Trader): T9: cost 79m. Upgrades to make it a good trader 30m. With another 12-15m in the bank you can trade (or have a couple of accidents)
Example (Explorer): Asp 6m. The drive and a good fuel scoop alone is gonna set you back 25m or so.
Example (Fighter): A kitted Vulture will be somewhere around 20m (and it costs like 2.5m?)...and there's no point in flying a non-kitted fighter.
Example (Miner)...erm..haven't tried that in a while, so I have no clue. But I guess that one should be rather cheap to kit.
Most of what you have is good, except for the mining ship.. Cheap is not a word i'd use to describe a half decent mining ship.
Yes you can go out there with a basic hauler for a 160k or so, but a cobra will set you have at least 1 million creds, and then some - as the type 4A refinery is a killer at 4.5 million creds!
have a look at this one i made up
http://www.edshipyard.com/#/L=702,5Rr5RrH7yH7y,2-6u6u6u5K5K5K6k,0720720bg7dg03w5PU
And it's nothing special, really!
I personally use my Python for mining, its got enough guns, shields and armour to shake off most pirates.
The important thing is to remember that you are going to lose 1 or 2 guns as mining lasers, unless you side with the power that has the combat mining lasers- I have no info on these (yet) about how good they are.
As to the original post, yes you ALWAYS need to budget for mess up in space and insurance costs associated with it.
Just assume every damn pirate is a kamikaze and wants to ram into your cockpit (not far wrong) and that every orbis station with arms wants to play golf with your ship.
If you are looking to upgrade, i`d suggest that you look on
http://www.edshipyard.com/ and do a basic overview of your new ship, then stick some goodies into it, and see what the price tag is...
For combat, stick a lot of stuff on it, as you want it pretty tough to start with + funds for death.
For trade you'll need the ship + insurance
AND cargo trade funds.
Remember that you are going to need roughly 1.2 million creds per 100 tons of cargo as a basic rule of thumb for decent trade funds. Add this to your ship cost + insurance.
If you can afford all the above, then good... if you want to risk it and run without insurance, be prepared to cry at your own stupidity when the pirates kill you or that evil space dock suddenly decided that you needed to hit the boost button at the wrong time..usually with a full cargo of palladium (they have secret scanner i swear).
TLDR
Dont be a idiot and ALWAYS have insurance costs + a bit more as bad things happen.