1) It has been a long time since I visited you (at the hotel).
I visited you at some (distant) point in the past.
2) It has been a long time since I used to visit you (at the hotel).
In the past I visted you on a regular basis, maybe once a week. At some (distant) point in the past, I broke with that habit.
3) It has been a long time since I have visited you (at the hotel).
I visisted you at some (distant) point in the past. I probably have visted you more than once, but that doesn't mean it was a habit.
So, yes, 2) and 3) could have a similar meaning, but 2) really draws attention to the fact that the visiting was happening on a regular, habitual basis, and it is the habit that stopped a long time ago.
Just for illustration, let's look at a different example.
Suppose I used to live in city A, but I have now moved to another place. While I lived in city A, I visted a certain restaurant once. Also, I was a regular at a bar (I was there almost every day). There was a cinema too. I went there a couple of times, but I'm no great fan of the cinema.
Now, after some years, I could say:
It's been a long time since I visted that restaurant. It was a really great experience though, maybe I should go back there some day.
It's been a long time since I used to frequent that bar. Nowadays I just drink alone, at home...
It's been a long time since I have been to that cinema. I don't know if that nice girl still works there.
This is a present perfect passive construction:
has been seen
Been is not the "past tense" of BE: it is its past/passive participle—let's abbreviate that PaPpl.
The preceding first verbform in the construction is has, a present-tense form of the perfect auxiliary HAVE. This auxiliary requires the following verb to take the PaPpl form, thus building a perfect construction.
Similarly, the BE here, in its PaPpl form been, is the passive auxiliary, which also requires a following PaPpl to build the passive construction: in this case, seen, the PaPpl of the final, lexical verb in the construction, SEE.
Best Answer
All three sentences are colloquially correct when spoken, and totally unambiguous. B would sound more formal because of the words "has been", but otherwise their meanings are all the same.
However, C is the only one which is correct in writing. The phrase "since I have done this…" is (I think) only properly correct when the word "since" is interpreted as "because", as in "Since I've eaten this pie, I'm not hungry any more". It sounds a bit clumsy even in this context.
Personally, in writing, I would prefer to mix B and C:
And in speech, I would contract "it has":
In speech and informal writing, the word "last" could optionally go at the end instead, but it reads a bit oddly in very formal writing: