The only synonyms I can think of are high and good, but they seem incorrect.
PS: I am trying to avoid "a lot of".
English Language Learners Stack Exchange is a question and answer site for speakers of other languages learning English. It only takes a minute to sign up.Sign up to join this community
You can use "much", but not by itself. The following is grammatical:
I have so much money
If you really wanted a single word, you can use the idiomatic phrase "big money":
I have big money.
Or the dominantly British "good money":
I have good money.
You can also say:
I have lots of money
I have tons of money
I have boatloads of money
I have much money.
The sentence isn't ungrammatical, but it sounds unusual or too formal.
Much is mainly used in negative and interrogative sentences as follows:
I don't have much money.
Does he have much money?
As for another single word in place of much, you can say:
I have considerable money
I have money galore.
There may some more adjectives, but I think all of them are not as idiomatic and common as the phrases a lot of, a large/considerable amount of, plenty of, etc. as follows:
I have a lot of money
I have a large amount ot money.
I have a considerable amount of money.
I have plenty of money.