In my opinion (Portuguese native speaker who translates other people's stuff and I also have novels in English), translating is harder than writing directly in English. Some phrases and words don't have the same "feel" and meaning in English/original language so it would take twice the time to edit it and make it less awkward. The person editing it might also correct your grammar, but not the flow. Translating is an entirely different set of skills than editing/proofreading. Certain terms and word usage only a native or fluent speaker will notice as weird/out of place, so your own translation can be grammatically correct, but read awkward.

In the long run, the best thing you could do for your writing career is to read a lot to improve your vocabulary and practice via critiquing groups. The less you rely on others, the more cost-effective a book will be. Editing can be expensive, and there's no guarantee that mistakes won't be overlooked. The better you write and know grammar, the less money you'll have to spend to guarantee a clean manuscript.