Been down that road before. Make sure your inflatable has a solid board at the back of it for you to mount the lecky. I managed to fit one on my cheapish inflatable boat without the board, when you turn the motor onto full power, the props will pull under the boat:). So in the end I bought a small aristocraft, works a treat but very slow. Also make sure you get a decent battery, as you will tend to put it on the highest speed all the time and it sucks up battery big time. 

 A decent battery to suit will cost you anther $250 and as soon as you stick a motor on it the boat has to be regoed which is another $130 per annum, plus your fishing from a boat license(which you should already have) The only way you can use it powered without rego is in the fresh with your freshwater fishing license.

You don't need a fishing from boat licence for the river unless you are catching crabs

 Not sure where you got that info from jack, I was under the impression that to fish from a boat anywhere in wa you need a rfbl licence. 

In a State with a coast stretching more than 12,800 km, boating is a popular recreational pastime.

You will need a Recreational Fishing from Boat Licence (RFBL) for any fishing activity from a powered boat including:

• line fishing (handline, rod and line, squid jigging);
• catching crabs;
• spearfishing
• catching octopus*; and
• dip-netting for prawns.

* RFBL holders are now allowed to use ‘trigger traps’ to fish for octopus as part of a two-year trial exemption – but a number ofrules around the use of this gear applies.

You need an RFBL for these fishing activities even if you are returning your catch to the water. An RFBL is also required when a powered boat is used to transport your catch or fishing gear from a land-based fishing location, including an island or a sandbar. You must produce your licence when requested to by a Fisheries and Marine Officer.

You don’t need an RFBL if you are:

• Fishing from a boat without a motor; such as a row boat.
• Fishing from a licensed fishing tour operator’s vessel or fishing charter boat.
• Fishing with a person who holds an RFBL (see ‘bag and boat limits’ below).
• Taking part in a fishing activity for which you already hold a current licence, such as rock lobster or abalone fishing. For example, if you have a licence to fish for rock lobster and that is the only fishing activity taking place on the boat, you don’t need an RFBL.

The RFBL database of boat fishers helps us determine who is fishing, where and what they are catching. This information assists us in managing our fisheries.

The RFBL covers a 12-month period from the date of issue and costs $30 or $15 for concessions. You can buy or renew your licence atDepartment of Fisheries offices or online.

Our recreational fishing rules page gives more information about bag limits and other fishing rules that apply to boat fishers.

Since they were introduced in 2010, the sale of RFBLs has generated more than $7.5 million for the management and enhancement of the State’s recreational fishing.

Licence funds are spent on a number of initiatives of direct benefit to recreational fishers in Western Australia.