Hi there,
I would like to propose a user centred approach to designing the mockup (within your budget), so that it fully meets the needs of the target audience, instead of designing something that the designer thinks is great, but the users might disagree.
Firstly, I would like to have a brief conversation with you (skype or email) to discuss the project, the target audience, your main competitors. Then, I would create some user personas that illustrate typical users with their needs (I would try to find a way to get some actual data about the users, maybe interview some to get some info), as well as write some user stories, usage scenarios. Also, I would look at the competitors in order to see what mental models your target audience is likely to have because of using their booking systems. Then, I would create some mockups of the proposed layout and the booking process and test it on some users, if needed, the second iteration of prototyping would follow.
Thank you for your consideration.
Best Regards,
Kristina