In many instances, you can revive an abandoned patent application. It is surprisingly easy to revive an abandoned application (when possible) as it is just paperwork and extra PTO fees on top of attorney's fees. In order to be able to revive it, the abandonment must be unintentional or unavoidable. See the relevant regulations.
If you intentionally leave the application abandoned for some period of time due to lack of funds, then I think it is likely that you cannot revive it at a later time.
If you need to get extra time on a tight budget, and the application has not yet been abandoned, then you could file a continuation application to keep your rights alive, and let the original application go abandoned. Consult your patent attorney about this.