जिम की सदस्यता सस्ती है।

Because की / का / के agrees with the noun being possessed, not the possessor.

Here, the possessed thing is सदस्यता (membership), and सदस्यता is a feminine singular noun. So Hindi uses की:

• जिम की सदस्यता = the gym’s membership / membership of the gym

Compare:

• जिम का कमरा = the gym’s room / gym room → कमरा is masculine singular, so का
• जिम के नियम = the gym’s rules → नियम is plural, so के

So की is there because of सदस्यता, not because of जिम.

Because the adjective agrees with सदस्यता, which is feminine singular.

• सस्ता = masculine singular
• सस्ती = feminine singular
• सस्ते = masculine plural / some oblique contexts

Since सदस्यता is feminine, the adjective must also be feminine:

• सदस्यता सस्ती है = The membership is cheap

If the noun were masculine, you would use सस्ता:

• कोर्स सस्ता है = The course is cheap

A very literal breakdown is:

• जिम = gym
• की = of
• सदस्यता = membership
• सस्ती = cheap
• है = is

So the structure is basically:

gym-of membership cheap is

Natural English would be:

The gym membership is cheap
or
Membership at the gym is cheap

Hindi often places the main adjective before है, and possession is shown with का / की / के.

In this sentence, it most naturally means membership at the gym or the gym membership.

Literally, जिम की सदस्यता is a possessive structure, but in English we often express this idea more naturally as:

• gym membership
• membership at the gym

So even though Hindi uses a possessive-looking pattern, the meaning is the usual idea of a membership connected with that gym.

जिम is a borrowed word from English gym. Hindi uses many English loanwords, especially for modern places, technology, business, and lifestyle topics.

So this sentence is completely normal Hindi.

You may also hear very English-heavy speech like:

• जिम की मेंबरशिप सस्ती है

But सदस्यता is the more Hindi-based word for membership.

Yes. In everyday speech, many speakers would naturally say:

• जिम की मेंबरशिप sasti hai

That is very common in modern spoken Hindi, especially in cities.

The difference is mostly register:

• सदस्यता = more standard, more formal, more textbook-style Hindi
• मेंबरशिप = very common colloquial borrowing from English

Both are understandable. If you are learning standard Hindi, सदस्यता is a useful word to know.

Unfortunately, noun gender in Hindi often has to be learned along with the word. There are some patterns, but they are not always reliable.

For this noun, you can tell from the sentence:

• जिम की सदस्यता
• सदस्यता सस्ती है

Both की and सस्ती show that सदस्यता is feminine.

A good habit is to memorize new Hindi nouns together with a phrase that reveals gender, such as:

• यह सदस्यता अच्छी है
• नई सदस्यता
• सस्ती सदस्यता

That way, you learn the noun and its gender at the same time.

Hindi does not have articles like English a, an, and the.

So:

• जिम की सदस्यता सस्ती है

can mean:

• The gym membership is cheap
• Gym membership is cheap
• The membership at the gym is cheap

The exact English article depends on context. Hindi usually leaves that unstated unless something else makes it specific.

In standard complete Hindi sentences, है should be included:

• जिम की सदस्यता सस्ती है

In casual speech, people sometimes drop it, especially in conversation or headlines:

• जिम की सदस्यता सस्ती

But that sounds informal, incomplete, or context-dependent. For learners, it is best to keep है.

Because that would mean something slightly different.

• जिम की सदस्यता = gym membership / membership of the gym
• जिम में सदस्यता would sound more like membership in the gym, which is not the normal way to express this idea

Hindi usually uses की here because the membership is understood as something belonging to or associated with the gym.

So for gym membership, जिम की सदस्यता is the natural phrasing.

A simple pronunciation guide is:

jim kee sadasyataa sastee hai

More carefully:

• जिम = jim
• की = kee
• सदस्यता = sa-da-sya-taa
• सस्ती = sas-tee
• है = often like hai or a short heh, depending on accent and speed

One important point:
की has a long ee sound, not a short i.

It comes from सदस्य, which means member.

So:

• सदस्य = member
• सदस्यता = membership

This -ता ending often makes an abstract noun in Hindi, similar to endings like -ship, -ness, or -ity in English.

For example, very roughly:

• मित्र = friend
• मित्रता = friendship

So सदस्यता is the state or condition of being a member: membership.

Yes. Depending on context, Hindi speakers might also say things like:

• जिम की मेंबरशिप सस्ती है।
• इस जिम की सदस्यता सस्ती है। = This gym’s membership is cheap.
• इस जिम का शुल्क कम है। = This gym’s fee is low.

Your original sentence is correct and natural, especially in standard Hindi. The alternatives just shift the style a little.

The two biggest grammar points are agreement and possessive markers:

1. की agrees with सदस्यता

   • because सदस्यता is feminine

2. सस्ती agrees with सदस्यता

   • because the adjective must match the noun

So this sentence is a great example of how Hindi grammar often revolves around the gender and number of the main noun.

A useful pattern to remember is:

X की Y + feminine adjective + है

For example:

• स्कूल की फीस कम है।
• किताब की कीमत ज़्यादा है।
• जिम की सदस्यता सस्ती है।

This will help you build many similar sentences.