the advice given is sound.
If you take it to the person quoting the cheapest price usually they dont know whats going to be involved (if its significantly cheaper) and in the end it will cost you more.
Take it to one of the many known VAG indys and get them to take a look, their quote will be more but im confident that the price your quoted will be all you have to pay to resolve this issue for good.
You have been told off enough for booting it
I have been in a similar situation where funds are very tight and i need my car, guys on here gave the best advice, replace the lot rather than chasing what "might" be the issue. Fortunately for me replacing the fuel pump is nothing like the cost of replacing the engine. 3k fitted - the sale of all your salvageable bits might not be too harsh.
Get all the diagnostics done for a definitive cause and issue then way up the cost and benefits of solutions.