I think a better option would be https://99designs.co.uk/
You set a budget and make a contest. Digix did the same for their current website https://www.dgx.io/
A bunch of designers create the mock ups then the community votes for the best one.
This way you can probably get the most out of any budget is approved for this
Competitive and cost effective, I like it. No sense in paying too much and having to select a winner from the get-go. Let the Designers compete for the money. You guys know I am a big fan of such methods. The hungry will do a better job, for less money and in less time, 90% of the time.