What's the least expensive way to get an experience key? I'd like to try some development with it.

[Manifold Destiny]

I'd like to compare the performance of a game meter using external servers vs internal key servers.  Does the internal database produce a meaningful decrease in lag?

If it takes a full SIM to get one, what's the cheapest way to get the land?  I don't really care how bad the land is, just as long as I can use it for this purpose.

[Innula Zenovka]

All premium account holders can create one experience.    They don't need to own land.  The experience can run on any parcel in SL where the parcel-owner has authorised it.

To write scripts using experiences, you don't even need to be a premium member.    All that's necessary is that someone who owns an experience assigns a group to that experience, creates a group role with the ability "Experience Contributor" and invites you to the group with that role.

See https://community.secondlife.com/t5/English-Knowledge-Base/Experiences-in-Second-Life/ta-p/2744686 for further info.