Most C20B's already have an energy containment ring. Check your last overhaul paperwork to see if it has one. You can get the paperwork from the overhaul shop using the Work Order listed in your engine log books.
In the event you do not, In addition to the usual costs associated with a hot section overhaul, you will need to have your GP support modified in order for the Containment Ring to be inserted. If you are purchasing a used aircraft, it is definitely something to check.
AESIR, if you can have your number 1 and 2 nozzle overhualed for $1,000 I need the name of your component repair shop. If you have 1750 hours on a number 1 nozzle in a Jet Ranger, it probably does not flow very well. The number 1 nozzle is right next to the flame so it takes a lot of abuse. There are some PMA nozzles which are pretty good and a lot cheaper than RR nozzles. All Model 250 engines have a GP support. The GP support contains the number 1 and 2 wheels. Technically, if you are only doing a hot section, you can remove the hot section and send it in for overhaul or exchange without sending in the entire turbine, however the safe but more expensive route is to send the entire turbine section in.