First, check out this article describing how deep-sea fish can be conditioned to live at atmospheric pressure. The depths they talk about are in the tens of MPa (hundreds of atmospheres) range. Basically they find that slowly lowering the environmental pressure allows the fish to survive.
This is similar to the case of scuba divers. If they ascend quickly the expanding gasses in their body can be fatal, but ascending slowly gives the gas enough time to escape the body.
According to wikipedia, A spherical tank to hold 100 MPa of pressure made of, say, a composite material with an ultimate tensile strength of a few GPa would have a radius around 50 times its thickness, not unreasonable. So it would probably be possible for high-pressure beings to undergo a long period of decompression in such a tank, eventually being able to survive at near-atmospheric pressures in a sort of space suit (or even without the suit if they can survive with just 1 atmosphere pressure).
The one problem with a space suit is that any significant pressure tends to inflate the suit like a balloon, making it difficult to move. Even in zero gravity, astronauts tend to be exhausted by spacewalks just from having to bend the joints in their suits.
Note however that things like temperature and oxygen levels are less adjustable. The partial pressure of oxygen is the total pressure times the fraction of the atmosphere that is oxygen. Normal partial pressure is 21 kPa, below a certain value you will suffocate (limit is somewhere around value for the peak of Mont Everest (43 mmHg, or 5,7 kPa) - people can climb there without oxygen bottles, but it is hard and they cannot stay there), and above around 30 kPa the oxygen actually becomes toxic (slowly, diver can still spend 45 min at 160 kPa). Your beings would probably need to breathe a special mix of gasses, like how astronauts breathe a low-pressure, high-oxygen mixture in their space suits.