How can startups manage international patent protection?

Unfortunately there is no easy answer. Patents are territorial and therefore if you want to have patent protection in a particular country or countries, you need to have patents in place in that country or those countries.

One possible "short-cut" or means for possibly reducing costs in obtaining patents is through the PPH - Patent Prosecution Highway. This program, which is now in effect within many countries that cooperate with each other, effectively permits you to obtain a patent quickly in a country where you have filed a patent application if you have already secured a patent in another country. So, for example, we had secured a patent here in the US for a client, and we had also filed a patent application for the client in Singapore. When the Singapore patent application came up for examination, they initially rejected the application, which IMHO was totally in error because they had cited prior art which was no better than the prior art cited during the prosecution here in the US, but then when we informed them that we had already secured a US patent, the SPO agreed that if we were content to patent claims in Singapore which matched the claims that we had obtained here in the US, they would allow the Singapore application, which is precisely what happened. Hence, prosecution was quick and relatively inexpensive thanks to the PPH because all we had to do was to effectively submit the matching claims to the SPO, no further arguments were necessary, and the patent was granted.