I don't have a reference but some philologists and linguists have speculated that you could survive (explain who you are, ask for employment and food, etc.) in a foreign land with as few as 500 words. Henry C. Fenn, author of several language texts, felt that a vocabulary of 5000 words was sufficient to support learning new words by context, e.g. by conversing with natives and reading newspapers. In my own experience as a linguist and translator I found 5000 generic words plus about 2000 topical words (those popular for only a few years) sufficient for keeping up with current events. This gives you some idea of the vocabulary size you should be considering.
I agree that generating a vocabulary by simply making up alternates to the 5000 to 7000 most popular words in your native language is tedious and slow. Worse, it is not fun. Even more worse, the resulting language is at an elevated risk of being insipid and possibly silly.
I suggest that you first create a list of word elements, and then compose most of your vocabulary words by altering and conjoining these elements. If you read up on Grimm's Law, and how Proto-Indo-European (PIE) was reconstructed, you'll see what I mean.
Web-search "proto indo european word list" and build up a list of element meanings. Throw away the PIE words and substitute your own. You'll probably only need to make about 300 word roots.
Make up some rules about combining roots into words. You don't need to be perfect or complete because you are aping a process that takes place over millennia, during which the rules would change.
Make up some rules about how sounds might change over time, and apply them consistently across all words. For example: after generating 1000 or 1500 words, change all 'P' sounds in your element list to 'B' and all 'T' to 'D'.
Now -- here's how you relieve the tedium and labor, which is the point of all this: Since you are confident that you have a rational method for producing believable words, don't make up all 7000 words at once. Start with a few hundred, and after that, create new dictionary entries as you need them.
Whenever you need a word, you look it up in your dictionary. If it's not there, you generate it and add it to the dictionary at that time. Since you already have lots of rules for forming words, making up the new one will be quick.
If you don't want to be the sole authority on word formation, you can roll dice or write a randomizing computer program. If the language is being used in a role-playing game, the rule could be "First player to open the dictionary gets to generate the new word."
What about the 200 words you already have? Well consider this. English, although a PIE group language, is actually descended from two distinct branches, the Teutonic and the Romance. (That's why English spelling is so hard. Almost half of our words come from low German, Anglic, Danish, etc. and present a Germanic spelling, while almost half come from Latin, French, and Norman, and present an Old French spelling.)
So, if you have any words from your original 200, that you want to keep, that cannot be rationally derived from your element list, simply declare that they arose from a separate branch or even a separate proto-language.
I don't see how this could fail to be fun.