Before you spend money if your track has mylaps timing system and you have a mylaps transponder you can get live laptimes with just an app. (both the track system and your phone have to be connected to the Internet).

MYLAPS Speedhive by MYLAPS Sports Timing
https://appsto.re/be/NQF66.i

EDIT: I used this app when my local track was on mylaps: MYLAPS Practice Results by MYLAPS Sports Timing
https://appsto.re/be/fyj4N.i

This worked great.

Not sure which app is the current one for live timing, their app strategy is one confused mess.