If you go for SE-IR first and plan to take a conversion course to ME-IR after, it will be more expensive than taking the ME-IR course right away. 

In the first case you need 2 typeratings, the 5 hour TR for Single Engine and the 8 hour course for Multi Engine. Plus the exam for both type ratings. That's already 6 hours extra and than you need to do the 5 hour conversion course for ME-IR, so in total it's 11 extra hours.