These are quite difficult questions to answer. To start with I'm going to talk economy (which is what your question seems aimed at). Both Britain and Russia lacked economies that could match Germany. Britain because of the bombing/isolation, and Russia because it lacked industrialization to start with.

So how much was Lend Lease? About $50.1 billion according to the US. This amounts to approximately $760 billion today. Quite a bit more, if you consider that economies weren't nearly as big as they are today.

I struggled to find an exact figure of US-British Lend Lease, but every source definitely describes it as detrimental. Here is a comprehensive characterization: http://www.ibiblio.org/hyperwar/UN/UK/UK-Civil-WarEcon/UK-Civil-WarEcon-9.html

The US-Russian Lend Lease seems quite a bit more clear cut. To start with, Stalin remarked in 1943 that "Without American production the United Nations could never have won the war." A truly depicting quote, about Lend Lease's role. Once the numbers are looked at, we can see why. Of the $50.1 billion, Russia received 11.3 billion putting Russia in the second largest recipient behind Britain. In The Development of the Russian Iron and Steel Industry we see that Russian steel output started at 18,317,000 tons of steel per year in 1940 and declined to 12,252,000 tons per year in 1945 due to the war. On the other hand, in Major Jordan's Diaries we see that over 1 billion tons of various kinds of steel were given to Russia throughout Lend Lease. Meaning Russia received over 90% of it's steel from the US. This story is similar for most of Russia's resources, and can be equated to food sent to other allies.

Keep in mind their was reverse Lend Lease, about 5.6 billion mostly from the British Common Wealth. $2.1 million from Russia. Russia, however, did pay a settlement of $722 million in 1972. Other forms of repayment included the selling of Lend Lease equipment to Britain 10 cents on the dollar, counting equipment lost in battle as a common loss and in general just writing it off.

So my opinion: I think it's improbable that the Allies could have won WWII without the US economy, which presented itself in the form of Lend Lease. I find it unlikely that Germany could have successfully conquered all of the USSR, but would have stalemated the Soviet Union at the least. Considering Lend Lease materials were flowing well before the beginning of hostilities, this scenario becomes even more likely (in my mind). In the end, Britain would be contained to it's island, not conquered, but unable to remove Germany from mainland Europe. While Russia would be without sufficient supply to beat Germany back to Berlin. The desert would be a different story, as Germany never had a great ability to extend over waters, and Britain's materials would be mostly tied to defending it's own waters.

I hope this was helpful, here is the US government's link that I used.