Where is the C152 registered? Go and contact the relevant authorities and ask them if they will accept that STC for your aircraft. May not be needed but just to be sure. Then contact a maintenance organisation, perhaps the one that currently maintains your C152, and ask them for a quote to do the conversion. Some of your questions can perhaps be answered by Del-Air, but for the budget side of things, I would have a good chat with your maintenance provider. It would help if you can find a local firm that has done this kind of work before.
The STC is here by the way:
https://rgl.faa.gov/Regulatory_and_G...2?OpenDocument