What if there’s $5 millions dollars project, but there is only one bid received?

In certain cases generalization might not be a possible remedy. Certain technologies are copy-write and hence cannot be bid by different suppliers. I think in such a case a Singe Source Document is to be floated mentioning the reason of non-competitive bidding and negotiating with the available supplier based on certain and cross check of bid part by part. 

I do agree to the above responses and wish to add that, in such a scenerio, it will be prudent to readvertise and also verify the specifications so that they are not directing you to one manufacturing, avoid an advertisement with brand names so that you do not limit the scope.

Also you should ensure that the tender is open for a reasonable time, and try all mode of advertising to reach all corners with potential bidders. In addition one can check with end users they might know where to get the said goods and services. This is however, very common in highly specialised tasks, like for instance when the governing law stipulates that one body is authorised to handle one portifolio, taking for instance construction for government structures, some Countries really stipulates that all works should be done by the Ministry of Works, hence one quote might be acquired. However, in such a scenerio as a procurement guru, you can tape also from the market to get price indication so as to stregthening your bargaining position considering your will know the general market price.

Having tried all avenues but still one bidder available, here one will need to seek for a waiver to proceed with the sole supplier, clearing reflecting efforts done to secure quotes but in vain. The waiver should seek for approval to proceed with one quote and approval should be sought from those with authority and according to the approval limits bearing in mind the value of the job or contract. Once the waiver is fully approved, then proceed and do the contract with all risks covered in contract to avoid possible exposures. Engage, and continuosly monitor performance of such High Value Purchases.

In addition to above, we also need to review our specifications, timeline, and other terms and conditions to ensure that there might not be any unnecessary obstacle for participation by additional bidders.
The Value For Money principle is also to be kept in view while finally deciding about procurement.
I am of the view that unless the project is of very spcific technical nature for which bidders are not available, we must have some increased scope of competition and this is possible only through generalization of specifications etc.