Using various online fleet builders none of them seem to include the cost of the objectives in my list value. Is this an error in my interpretation of the numbers on the cards or their error in totalling the list points?

It is an error in interpretation.

The "Points" value listed on the bottom of the Card, is how many points each objective or victory token you earn through that objective is worth....

So, with fire lanes, for example, '15' is listed.

This does not mean 15 points to include in your list.

What this means is, when you play the objective, and earn a token by having the most battery dice to fire at a single point, that token you earn is worth 15 points at the end of the game... (Which means if you hold all 3 points, thats 45 points per turn, or 270 points over a full game if you're just that good....)

I thought this but some more experienced players told me otherwise .

You are being told wrong, then.

Page 9, RRG, "Scoring":

• Each victory token is worth the number of fleet points indicated in the lower-right corner of the objective card used for that game.

and

Page 13, RRG, "Victory Tokens"

Victory Tokens

Players may collect victory tokens as indicated by some objective cards and place them next to their ship cards. At the end of the game, each victory token increases the player’s score by the amount indicated on the objective card.\

and further:

Page 6, RRG, "Fleet Building"

The fleet point cost of each ship, squadron, and upgrade is printed in the lower-right corner of the card.

As part of building a fleet, each player must choose three objective cards, one from each category.

Notice that it does not reference the Objective Card as something that has a "cost" - only Ships, Squadrons and Upgrades.