What were the Pahrump parks that wanted over $2K for 30 days? Are you basing that on a daily rate or a monthly rate?
RV parks usually have a nightly rate, a weekly rate, and a monthly rate. For example, $25/night, $125/week, $300/month.
I'm not going to recommend any specific park, but the Pahrump area has resort parks and it has budget parks. Talk to the manager at one of the latter, and tell them what you are planning. They may give a discount, if you pay cash, and all you want is a 30 day receipt without staying the 30 days. Make sure you can get mail at the park's address.
The DMV rule only specifies a 30 day (1 month) receipt, not that one actually resides there for a month.
Out in Amargosa Valley there is a RV park, where one can get a street address that is acceptable to the DMV, that will be tied to a physical mailbox in the park.
There are only two RV parks in AV, it will be obvious which one will be amenable. [Hint: it is the one that isn't located at a casino on the California-Nevada border.]