I had the same problem. My 27 S has been stolen. It's been running me crazy. There is no way to buy an used 27 S – nobody would sell it…guess why.

I have tried 38 G, 48 G and 49 G. None of them will replace 27 S. 38 G is more a “school” type of calculator with lot of interesting mathematical functions and plotting capabilities, but heavy restrictions, such as one character variable names, no thousand separators, you can not assign names to equations and much more. 48 and 49 are by far too complicated for normal daily life and too large in size (both very powerful, 48 is nicely crafted in the old HP style, 49 more a game boy type, but working fine.).

I was advised in this forum to look into 19II b. A very good advice indeed. You get pretty close to 27 S. It has even some more functions than 27 S. Among others currency conversions, unit conversions and some plotting functions. I found two limitations so far – 1.the algebraic precedence seems not be so strict – you will need more brackets to be safe. 2. in the 2 variables statistics/regression you only are asked to select the X-variable. The Y- variable is the one that presently resides in the memory. Not a real problem, but somewhat confusing.

Should you buy one, make sure that it opens well. Some of the later models have a tendency to be really hard to open.