Low Cost In-building Coverage_UHF Radio

I have an Operational UHF Radio System (350-360Mhz). One Building does not have signal coverage, where users cannot communicate when inside the building.
The signal measured on the top of the building is (-75dBm). I know of the simple solution of using a BDA, BUT i do not want that. I am looking for a low cost solution.
I have an idea of using two Hi Gain Line Amplifiers with a 12 Directional Yagi Antenna as donor and leaky cable (7/8" Foil radiax w/Bump) inside the Building. One amplifier setup for the Downlink and the other amplifier setup for the Uplink. This will eliminate the need for a Duplexer.
I have not yet tried it. Does anybody know whether this will work or has anybody tried it before?
Or can somebody tell me of any other low cost solution?
Thank you Guys,

There are more details I can add to describe the case:

This is a 5-Channel MPT1327 Trunking , Single Site Radio System. The building in concern is made of highly isolated concrete. It is around 9 KM away from the site. It is not connected to the radio site (Fiber or else).
The problem in Hand Held communication inside the building is in both ways (Uplink & Downlink). The actual situation is that communications insdie the building is lost at most places. the Radio loses the Control Channel and starts scanning. The signal levels inside the building ranges from -95 to -100 dBm.
The frequencies of the system are as follows:

Base TX MHz Base RX MHz
350.5375 355.5375
350.5500 355.5500
350.5625 355.5625
350.5750 355.5750
350.5875 355.5875