So much this.

If I know I only need a tool once or twice, I always buy Harbor-Freight (discount power tools if you're not familiar with them). I've always been able to complete the job with it, and anything beyond that is just bonus IMO (versus renting a better tool for the job at equal or greater cost).

Normally, though, they last a lot longer than that. I bought a HF drill in like 2004 and it finally died last year and was used pretty heavily throughout its life. Pretty sure I got my $18 worth.