Investor for IP - what should be our strategy?

You probably have two choices: 1) somehow get enough funding without your investors - borrow the money from family, friends, mortgage your house if need be, think outside the proverbial box; 2) file provisional patent applications which are less costly to file but beware that even though they are provisional applications, they still need to completely, accurately, and thoroughly disclose the invention because your provisional applications will serve as priority documents for your later-filed non-provisional or PCT applications which must be filed within one year of the filing of your provisional applications.