Price Checks

I heard somewhere that a good rule of thumb is 320m isk per 1mil SP? Is this correct?

In the last year, the prices variated between 275 ISK / SP to 450 ISK / SP. I usually recommend a median price of 350 ISK / SP as a baseline, and from there look at the focus of the character, how well their core skills are etc. If some of the basics are bad, you substract money.

In the end, it depends on what the fool wants to pay for a toon.

I look at it this way.

1.5 M sp per month on average.
The amount of total SP divided by 1.5 reveals how many months of training a character has had.
Take that amount and see how much PLEX that is.
Include a little bit for skillbooks.

And then some people would like the transfer costs covered in the sale.

Of course, this is a baseline optimum for the seller, supply and demand makes it vary quite a bit.

Also, some types of pilots are worth more by default, simply because they have the skills they need to make isk.

A very good PI character can sell for way more then its SP would suggest, if the buyer lives in nullsec or a wormhole.
PI in nullsec and wormholes delivers enough passive isk per month, that that alone can support the entire account.

Indy toons (the ones that can build stuff efficiently) can also easily support themselves, which means they can make their investment back rather quickly.

Mining pilots have lost a lot of value lately, simply because of the ISBoxer thing, this has caused many people to want to sell their miners and this causes an oversupply.

I recently sold a perfect Proteus pilot for a LOT more then he is "worth", but this is because perfect Proteus pilots are quite rare on the market, as opposed to Tengu pilots for example.