Why is there only one channel tunnel?

(I do have a serious query at the end)

I was trying to lay track in a straight line and despite the use of a straight tracksetta and then the edge of a quality one metre level, I was still veering one way or the other after a meagre 4 or 5 feet. From where I was laying the track everything seemed fine until I made two checks:-

1) Can I still fit the other running line, platform and two outer tracks in the space left before everything falls off the edge of the baseboard? If not, start again.
2) If I walk to the end of the line and cast my eye can I see a kink? If yes, start again.

Twice these checks failed and each time the deviation was barely perceptible at the point it started, neither did the straight edges I was using show it up.

Whilst pondering on my difficulty of keeping straight over a distance of 12 feet I wondered how you got to the moon without missing by rather a long way. Then I decided that it didn't matter, you just kept adjusting your course so that you were pointed at the moon, after all it is rather large and you can see it. But then I wondered what if you can't see your target such as the other half of a tunnel. A fraction of a degree off and as the joke about the 2 man quote to build a tunnel goes - "If we miss, then you get two tunnels for the price of one".

I realised that the Chunnel builders probably used GPS and lasers. But I didn't think that GPS would work to the tolerance I needed, though a laser level was a possibility. A quick google showed that basic models can be had for about £20 from Amazon but that still seemed like overkill, so before nipping down to B & Q I tried one last ploy.

I performed my number 1 check above at 4 foot intervals and secured a 4 inch piece of offcut track where the outer rail should be. Then I got a long half inch wide measuring tape - the kind builders use, it's about 28 ft long and doesn't like to kink left or right - and laid it between the rails of the 4 inch offcuts. Now I was able to use the tape as a guide to laying the track I wanted without any further dramas. The result is completely straight - a bit like the track from the opening of Once upon a time in the west - but it's near enough and once a train is standing on it you don't notice.

Query:
Whilst on (or near) the subject of the channel tunnel, I was thinking of using it this summer but I don't quite understand why there is a reasonable price and totally out of this world price. What are you not getting for the cheap fare? I have heard that maybe you get to wait a lot for some trainspotting if you haven't paid the ransom. Is this true?

David